Industrial Environmental Restv.rc'1  : !"'*'
                on  Laboratory          ' '• ' -
                  Research Triangle Park NC 277' 1
vvEPA
Operation  and
Maintenance  of
Participate Control
Devices in Kraft Pulp
Mill and  Crushed Stone
Industries

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                    RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental Protec-
tion Agency, have been grouped into nine series. These nine broad categories were
established to facilitate further  development and application of environmental tech-
nology. Elimination of traditional grouping was consciously planned to foster technology
transfer and a maximum interface in related fields. The nine series are:

          1. Environmental Health Effects Research
          2. Environmental Protection Technology
          3. Ecological Research
          4. Environmental Monitoring
          5. Socioeconomic Environmental Studies
          6. Scientific and Technical Assessment Reports (STAR)
          7. Interagency Energy-Environment Research and Development
          8. "Special" Reports
          9. Miscellaneous Reports

This report has been assigned to the ENVIRONMENTAL PROTECTION TECHNOLOGY
series. This series describes research performed to develop and demonstrate instrumen-
tation, equipment, and methodology to repair or prevent environmental degradation from
point and non-point sources of pollution. This work provides the new or improved tech-
nology required for the control and treatment of pollution sources to meet environmental
quality standards.
                             REVIEW NOTICE


          This report has been reviewed by the U.S. Environmental
          Protection Agency,  and approved for publication.  Approval
          does not signify that the contents necessarily reflect the
          views  and policy of the Agency, nor does mention of trade
          names or commercial products constitute endorsement or
          recommendation for use.
          This document is available to the public through the National Technical Informa-
          tion Service, Springfield, Virginia 22161

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                                     EPA-600/2-78-210

                                          October 1978
   Operation and  Maintenance  of
Participate Control Devices in  Kraft
    Pulp Mill and  Crushed  Stone
                   Industries
                          by

                   M. F. Szabo and R. W. Gerstle

                 PEDCo. Environmental Specialists, Inc.
                     11499 Chester Road
                     Cincinnati, Ohio 45246

                     Contract No. 68-02-2105
                      ROAP 21ADL-037
                   Program Element No. 1ABO12


                 EPA Project Officer. Dennis C. Drehmel

               Industrial Environmental Research Laboratory
                 Office of Energy, Minerals, and Industry
                  Research Triangle Park, NC 27711
                        Prepared for

               U.S. ENVIRONMENTAL PROTECTION AGENCY
                  Office of Research and Development
                     Washington, DC 20460

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                            ABSTRACT





     Control of fine particulate emissions from selected kraft




pulp mill and stone crushing facilities is addressed.  The




principal devices considered are electrostatic precipitators,




wet scrubbers, and fabric filters.   Guidelines are provided for




industrial personnel responsible for selection of an appropriate




control device.  Information on the operation and expected per-




formance of conventional air pollution control devices is based




on current design practice, theoretical design models, reported




performance, cost predictions,  and published information.

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                        TABLE OF CONTENTS


                                                            Page

Abstract                                                     ii

Figures                                                      vi

Tables                                                        x

Acknowledgment                                              xiv

1.0  Introduction                                           1-1

     1.1  Purpose of Report                                 1-1

     1.2  Significance of Particulate Emissions             1-1

     1.3  Scope of the Report                               1-2

2.0  Control Systems:   Parameters and Correlations          2-1

     2.1  Emission Sources, Characteristics,  and
          Control Systems                                   2-1

     2.2  Evaluation of Various Control Alternatives        2-43

     2.3  Electrostatic Precipitators                       2-43

     2.4  Mechanical Collectors                             2-81

     2.5  Wet Scrubbers                                     2-84

     2.6  Fabric Filters                                    2-100

3.0  Operation and Maintenance of Particulate
     Control Devices                                        3-1

     3.1  Operation and Maintenance of Electrostatic
          Precipitators                                     3-1
                               111

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                 TABLE OF CONTENTS  (continued)


                                                            Page

     3.2  Maintenance and Operation of Mechanical
          Collectors Servicing Bark/Fossil-Fuel Boilers     3-16

     3.3  Operation and Maintenance of Wet Scrubbers        3-20

     3.4  Operation and Maintenance of Fabric Filters       3-35

4.0  Fractional Efficiency Relationships                    4-1

     4.1  Introduction                                      4-1

     4.2  Procedures for Determining Fractional
          Efficiency Performance                            4-2

     4.3  Efficiency Relationships for Fabric Filters       4-20

5.0  Summary and Conclusions                                5-1

     5.1  Design Parameters                                 5-1

     5.2  Operation and Maintenance                         5-9

     5.3  Fractional Efficiency Relationships               5-11

     5.4  Costs                                             5-14

Appendix A-l  Installation Lists for Particulate Control
              Devices on Kraft Pulp Mill Applications       A-l

Appendix A-2  Capital and Annual Costs of Precipitators
              for Pulp Mill Applications                    A-10

Appendix A-3  Checklist for Obtaining Design and
              Operating Data on Particulate Scrubbers
              (Design and Operating Parameters)             A-17

Appendix A-4  Capital and Annual Costs of Venturi
              Scrubbers on Kraft Pulp Mill and Crushed
              Stone Industry Processes                      A-20
                               IV

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                 TABLE OF CONTENTS (continued)
                                                            Page
Appendix B-l  Electrostatic Precipitator Subsystem and
              Component Function and Operation              B-l

Appendix B-2  Preoperating Checklist for Precipitators      B-15

Appendix B-3  Electrostatic Precipitator Inspection,
              .Maintenance, and Troubleshooting Procedures   B-20

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                         LIST OF FIGURES


No.                                                         Page

2-1    Kraft Pulping Process                                2-2

2-2    Principal Design of Recovery Boiler Furnace          2-5

2-3    Direct-contact  (Conventional) Recovery Furnace
       System with Black Liquor Oxidation                   2-6

2-4    Indirect-contact Recovery Furnace System             2-7

2-5    Material Flows Through a Typical Crushed Stone Plant 2-26

2-6    Particulate Size Distribution from Rock Processing
       Operations                                           2-31

2-7    Combination Wet Suppression Dry Collection Systems   2-35

2-8    Wet Dust-suppression Systems                         2-37

2-9    Hood Configuration Used to Control a Cone Crusher    2-41

2-10   Sectionalization of a Precipitator                   2-55

2-11   High Tension Splits                                  2-58

2-12   Plot of K Versus -ln(l-r,) for Recovery Furnace
       Applications                                         2-68

2-13   Selected Precipitator Correlations for
       Conventional Kraft Pulp Mill Recovery Furnaces       2-72

2-14   Selected Precipitator Correlations for Low-odor
       Kraft Pulp Mill Recovery Furnaces                    2-77

2-15   Selected Precipitator Design Correlations for
       Bark Combination Fossil Fuel Fired Boilers           2-81

2-16   Typical Fractional Efficiency Curve                  2-85

2-17   Venturi Flooded Disc Scrubber System                 2-101
                               VI

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                   LIST  OF  FIGURES  (continued).


 No._                                                         Page

 2-18     Exhaust  Gas  Volumes  at  Various  Plant  Capacities      2-119

 2-19     Cost-effectiveness of Fabric  Filter Systems  for
         Model  Processes                                     2-127

 3-1     Wet  Bottom Electrostatic Precipitator with Heat
         Jacket                                              3-5

 3-2     Research-Cottrell  Flooded  Disc  Scrubber              3-22

 3-3     Reverse  Air  or  Shaker Type                          3-37

 3-4     Pulse  Jet  Type                                       3-38

 3-5     Diagram  Showing Normal  Operation  and  Shake
         Cleaning of  a Fabric Filter                          3-40

- 3-6     Schematic  for Reverse Flow Cleaning During
         Continuous Filter  Operation                          3-42

 3-7     Poppet Valve                                        3-51

 3-8     Typical  Trough  Hopper and  Screw Conveyor
         Arrangement                                          3-54

 3-9     Bag-cell Plate  Attachments                          3-55

 3-10     Typical  Shaker  Arrangement                          3-59

 4-1     Predicted  Precipitator  Penetration for Conven-
         tional and Low-odor  Recovery  Furnaces.               4-4

 4-2     Predicted  Precipitator  Penetration for Conven-
         tional and Low-odor  Recovery  Furnaces.               4-6

 4-3     Predicted  Precipitator  Penetration for Conven-
         tional and Low-odor  Recovery  Furnaces               4-7

 4-4     Measured and Theoretically Calculated Fractional
         Efficiency of  an ESP on a  Kraft Pulp  Mill
         Recovery Boiler                                     4-9

                                vii

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                  LIST OF FIGURES  (continued)
No.                                                         Page
4-5     Penetration as a Function of Particle Size for
        an ESP on a Kraft Pulp Mill Recovery Boiler         4-10

4-6     Fractional Collection Efficiency of Precipitator
        Collecting Particulate from Pulp Mill Recovery
        Boiler                                              4-11

4-7     Predicted Precipitator Penetration for Bark/Fossil
        Fuel-fired Boilers                                  4-14

4-8     Predicted Precipitator Penetration for Bark/Fossil
        Fuel-fired Boilers                                  4-15

4-9     Predicted Precipitator Penetration for Bark/Fossil
        Fuel-fired Boilers                                  4-16

4-10    Predicted Penetration for Venturi Scrubbers on
        Sludge Lime Kilns                                   4-19

4-11    Predicted Penetration for Venturi Scrubbers on
        Jaw Crushers                                        4-21

4-12    Predicted Penetration for Venturi Scrubbers on
        Conveyors and Screens                               4-22

A.2-1   Capital Investment for Precipitators on
        Conventional  (High-odor)  Recovery Furnaces          A-ll

A.2-2   Annual Costs for Precipitators on Conventional
        (High-odor)  Recqvery Furnaces                       A-12

A. 2-3   Capital Investment for Precipitators on
        Low-odor Recovery Furnaces                          A-13

A.2-4   Annual Costs for Precipitators on Low-odor
        Recovery Furnaces                                   A-14

A.2-5   Capital Investment for Precipitators on Bark
        Combination Bark Fossil Fuel-fired Boilers          A-15
                              VI11

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                  LIST OF FIGURES (continued)
No.                                                         Page

A.2-6   Annual Costs for Precipitators on Bark
        Combination Bark Fossil Fuel-fired Boilers          A-16

A.4-1   Effects of Collection Efficiency and Gas Rate
        on the Capital Investment of Venturi Scrubber
        Systems for Lime Kilns                              A-21

A.4-2   Effects of Gas Rate, Electricity Usage,  Fixed
        Charges, and Others on the Annual Costs  of
        Venturi Scrubber Systems for Lime Kiln              A-22

A.4-3   Effects of Collection Efficiency and Gas Rate
        on the Capital Investment of Venturi Scrubber
        Systems for Stone Crushers                          A-23

A.4-4   Effects of Gas Rate, Electricity Usage,  Fixed
        Charge, and Others on the Annual Costs of
        Venturi Scrubber Systems for Stone Crushers         A-24

A.4-5   Effects of Collection Efficiency and Gas Rate
        on the Capital Investment of Venturi Scrubber
        Systems for Stone Crushing Conveyors                A-25

A. 4-6   Effects of Gas Rate, Electricity Usage,  Fixed
        Charges, and Others on the Annual Cost of
        Venturi Scrubber Systems for Stone Crushing
        Conveyors                                           A-26

B.l-1   Insulator, Vibrator-rapper Assembly, and
        Precipitator High-voltage Frame                     B-4

B.I-2   Precipitator Insulator and Vibrator-rapper
        Assembly                                            B-5

B.I-3   SCR Mainline Control                                B-6

B.l-4   Discharge Electrode Unshrouded                      B-13

B.l-5   Discharge Electrode Shrouded                        B-13

B.l-6   Precipitator Collecting Electrodes                  B-13


                               ix

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                         LIST OF TABLES
No.                                                         Page

2-1    Typical Gas Characteristics In Kraft Pulp Mill
       Processes                                            2-11

2-2    Characteristics of Particulate Emissions from
       Selected U.S.  Power Boilers                          2-12

2-3    Typical Particle Size Distribution of Fly Ash
       from Bark/Fossil-fuel Boilers                        2-17

2-4    Reported Uncontrolled Emissions Versus Emission
       Factors                                              2-29

2-5    Factors Bearing on Control Device Selection          2-45

2-6    Parameters Affecting Precipitator Design             2-46

2-7    Design Power Density                                 2-50

2-8    Design Parameters and Design Categories for
       Electrostatic  Precipitators                          2-51

2-9    Typical Operating Conditions for Precipitators
       on Conventional Recovery Furnaces                    2-62

2-10   Nomenclature for the Electrostatic Precipitator
       Computer Model                                       2-64

2-11   Typical Electrical Operating Data on Standard
       9-inch Plate Precipitator with 0.109-inch Discharge
       Electrodes                                           2-70

2-12   Differences in Particulate Properties in
       Conventional and Low-odor Recovery Processes         2-73

2-13   Typical Analysis of Flue Gas from Conventional
       and Low-odor Recovery Boilers                        2-74

2-14   Typical Operating Conditions in Precipitators
       on Bark/Fossil-fuel Boilers                          2-78

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                   LIST OF TABLES (continued)


No.                                                          Page

2-15   Parameters Affecting Cyclone  Design                  2-84

2-16   Performance Trends Based on Changes in  Cyclone
       Design                                               2-87

2-17   Effects of Physical Properties and Process  Variables
       on Efficiency                                        2-88

2-18   Operating Characteristics of  Particulate Liquid
       Scrubbers on Kraft Lime Kilns                        2-89

2-19   Performance Characteristics of Showered Mist
       Eliminators on Smelt Dissolving Tanks                2-93

2-20   Design Parameters for Kraft Pulp Power  Boiler
       Baghouses                                            2-103

2-21   Process Facilities Controlled by Baghouse Units
       Tested                                               2-105

2-22   Characteristics of Fabric Filter Cleaning Methods    2-109

2-23   Characteristics of Various Fabrics                   2-112

2-24   Annual Cost Components for Fabric Filter Control
       System                                               2-118

2-25   Characteristics of Exhaust Gas from Model Sizing
       and Transfer Operations                              2-120

2-26   Capital and Annual Costs of Fabric Filter Systems
       for Model Sizing and Transfer Operations             2-121

2-27   Capital and Annual Costs of Wet Dust-suppression
       Systems for Crushers, Screens, Transfer Points,
       and Crusher Feeds                                    2-124

2-28   Capital and Annual Costs of Combination Fabric
       Filters and Wet Dust-suppression Systems for
       Crushers, Screens, Transfer Points, and Crusher
       Feeds                                                2-126


                               xi

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                   LIST OF TABLES  (continued)
No.                                                         Paqe
3-1    Comparison of Design and Operational Features of
       Utility and Kraft Pulp Mill Electrostatic
       Precipitators                                        3-10

3-2    Major Maintenance Problems with Utility,
       Metallurgical, and Paper Mill Precipitators          3-15

3-3    Scrubber Maintenance                                 3-31

3-4    Spare Parts Inventory for Venturi Scrubber           3-32

3-5    Manpower Requirements for Maintenance Involving
       Plugging and Scaling of Venturi Scrubber             3-33

3-6    Type of Maintenance Required - Venturi Scrubber
       Systems                                              3-34

3-7    Checklist for Routine Inspection of Baghouse         3-47

3-8    Baghouse Collector Maintenance                       3-49

3-9    Approximate Cost of Replacement Bags                 3-56

3-10   Bag Life in Kraft Pulp Mill and Crushed Stone
       Applications                                         3-56

3-11   List of Replacement Parts for a Baghouse Filter      3-57

4-1    Summary of Inlet Particle Size Distribution Data
       Used in ESP and Scrubber Prediction Models           4-2

4-2    Baghouse Particulate Efficiencies - Survey Data      4-24

4-3    Baghouse Particulate Control Efficiencies on
       Crushed Stone Industry Processes                     4-28

5-1    Evaluation of Dry ESP's for Kraft Pulp Mill
       Recovery Boilers and Bark/Fossil-fuel Boilers        5-3
                              XII

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                   LIST OF TABLES (continued)
No.                                                          Page

5-2    Evaluation of Venturi Scrubbers for Kraft Pulp
       Kill Lime Kilns and Crushed Stone Processes          5-4

5-3    Evaluation of Fabric Filters for Kraft Pulp
       Mill Bark/Fossil-fuel Boilers and Crushed
       Stone Processes                                      5-5

A.1-1  Selected Research-Cottrell, Inc. Pulp Mill
       Recovery Precipitators                               A-2

A.1-2  Installation List for Wet Scrubbers on Bark
       Boilers                                              A-6

A. 1-3  Installation List for Bark/Fossil Fuel Boilers       A-7

B.3-1  Troubleshooting Chart for Electrostatic
       Precipitators                                        B-40

B.3-2  Frequency of Failure and Repair Times Required
       for Various Precipitator Components                  B-43
                              Xlll

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                    METRIC CONVERSION FACTORS
    To convert
  English units

British thermal unit  (Btu)

Cubic foot  (ft )

Degrees fahrenheit

Foot

Gallon  (U.S. Liquid)

Gallon  (U.S. Liquid)

Grain (gr)

Horsepower  (hp)

Inch

Inch

Inches of water

Pound

Ton, short
   Multiply
     by

    1054

  0.0283

5/9 (°F-32)

  0.3048

  0.0038

  3.7854

  0.06479

  746.0

  0.0254

  2.54

  248.8

  0.4536

  0.9C72
Some Common Physical Constants


Boltzmann's constant

Gravitational acceleration

Universal gas constant

Electron volt

Standard temperature =

and pressure (STP)
     To obtain
     SI units

Joule  (j)

Cubic meter  (m )

Degrees Celsium  (C]

Meter  (m)

Cubic meter  (m )

Liter  (1)

Gram (g)

Watt (w)

Meter  (m)

Centimeter  (cm)

Pascal  (pa)

Kilogram  (kg)

Metric ton(kkg)
   k = 1.3805 x 10~23 J/°K

   g = 9.807 m/s2

   R = 8.304 J/mol-°K

   eV = 1.602 x 10~19 J

   1.013 x 105 Nt/m2
   and 273.15°K
                               XIV

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                         ACKNOWLEDGMENT






     This report was prepared for the Industrial Environmental




Research Laboratory, U.S.  Environmental Protection Agency,  Re-




search Triangle Park, North Carolina, by PEDCo Environmental,




Inc., of Cincinnati, Ohio;  Cottrell Environmental Sciences  (CES),




Research-Cottrell,  Inc.,  Somerville, New Jersey; and Midwest




Research Institute,  Kansas  City,  Missouri.




     The project director  was Mr. Richard W.  Gerstle, and the




project manager was Mr.  Michael F.  Szabo.  PEDCo Environmental,




Inc., as the primary contractor and editor,  directed and coordi-




nated the project and also  provided technical information.




     Cottrell Environmental Sciences researched and coordinated




the information on electrostatic  precipitators and wet scrubbers.



The work was managed and executed by Mr. David V. Bubenick  with




the help of Mr. Chin T.  Sui,  Dr.  P.O. Paranjpe, and Mr.  Manuel




Canton.  The CES effort  was directed by Drs.  Paul L. Feldman and.




Richard S.  Atkins.




     Midwest Research Institute evaluated the fabric filtration




systems.  Principal investigator  was Mr. Mark A. Golembiewski,




assisted by Mr. V.  Ramanathan.  Program supervision was provided




by Dr. K.P. Ananth.
                               xv

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                            SECTION 1




                          INTRODUCTION





1.1  PURPOSE OF REPORT




     This report is intended to provide guidelines by which en-




vironmental control personnel in the kraft pulp mill and crushed




stone industries can  (1) determine which type of particulate




control device is best for a certain process, (2) follow opera-




tional and maintenance practices that will maintain high partic-




ulate collection efficiencies and minimize malfunctions, and  (3)




relate the total mass efficiencies of control devices to their




efficiencies for collection of particulate in specific size frac-




tions .




1.2  SIGNIFICANCE OF PARTICULATE EMISSIONS




     Many undesirable effects have been related to the discharge




of particulate matter into the atmosphere.  Particulates consti-




tute a health hazard, cause poor visibility, function as a trans-




port vehicle for gaseous pollutants, and  (in many cases) are




highly active both chemically and catalytically.




     The full effects of submicron particulates on health are not




yet well defined.  They are regarded as constituting a whole




category of pollutants rather than being a single pollutant.




Once dispersed, they behave  (depending on size)  similarly to




coarse particles and gases.  They remain suspended and diffused,





                               1-1

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are subject to Brownian motion,  follow fluid flow around obsta-

cles,  and can penetrate deep into the respiratory system.

     Particles larger than 5 urn diameter are deposited in the

nasal  cavity or nasopharynx.  Increasing numbers of smaller

particles, so minute that they are difficult to measure, reach

the lungs.  More than 50 percent of particles between 0.01 and

0.1 um that penetrate the pulmonary compartment are deposited in

the lungs.  This tendency to penetrate and be captured in the

respiratory system is more a function of the geometry of the

particles than of their chemical properties.

     The unhealthy effects of these captured fine particulates

are largely due to their chemical or toxic qualities, although

the physical properties of certain long, fibrous materials may

also irritate tissue.  Many unknown factors remain, however, so

it is  unwise to generalize concerning the dangers of fine parti-

culates .

1.3  SCOPE OF THE REPORT

     This study deals with the following major emission sources

in the kraft pulp and crushed stone industries:

     Kraft pulp                         Crushed stone

     Recovery furnaces                  Crushers
     Lime kilns                         Screens
     Smelt dissolving tanks             Transfer points
     Combination bark/fossil-fuel-      Storage bins
      fired boilers                     Drilling equipment

     Information presented in this report was obtained from

review of current literature, site visits, and personal communi-

cations with manufacturers and users of control equipment.
                               1-2

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     The following high-efficiency particulate control devices




are evaluated:  electrostatic precipitators (ESP's),  wet scrub-




bers, and fabric filters (baghouses).   Cyclone collectors,




although not highly efficient, are evaluated to a limited extent,




because of their historical use as a primary control  device and




their present use in controlling coarse particle size distribu-




tions.




     In the kraft pulp mill industry,  fabric filtration systems




are not used to control particulate emissions from recovery




furnaces, lime kilns, or smelt dissolving tanks.  Emissions from




these sources are controlled primarily by wet scrubbers or ESP's.




All four of the control devices are used, however, on combination




bark/fossil-fuel boilers.




     In the crushed stone industry, fabric filters are used




almost exclusively for controlling emissions from rock processing




operations.  Wet suppression techniques are used either separa-




tely or in conjunction with baghouses  to limit fugitive emissions.




Wet scrubbers are also used on stone crushing and conveying




operations.



     Section 2 provides descriptions of the subject processes and




discussion of the extent of usage of conventional control devices




to collect their particulate emissions.  It then considers




control system design parameters and basic design philosophies.




Some correlations between design parameters are given, as well as




estimates of capital and annual costs  of each control device.
                               1-3

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     Section 3 describes the operation of each control  device and




the maintenance and operational procedures that contribute  to




operation at maximum efficiency with minimum downtime.   The dis-




cussion encompasses startup, shutdown, normal operational proce-




dures, and common malfunctions.




     Fractional collection efficiencies of precipitators, wet




scrubbers, and fabric filters are discussed in Section  4.  Com-




puter models are used to predict the fractional efficiency  per-




formance of dry precipitators and venturi scrubbers on  kraft pulp




mill and crushed stone operations.   Almost no test data are




available for comparison with the models.  The fractional effi-




ciency relationships of fabric filters are discussed only briefly




because an appropriate computer prediction model is not avail-




able.  Only one set of fractional efficiency test data  were




available for a mobile fabric filter.




     Section 5 presents conclusions on the design, operation,




maintenance, and the fractional efficiency capabilities of  the




particulate control devices, including a comparison of  the  ad-




vantages and disadvantages of applying each type of control




device to the subject industries.
                               1-4

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                REFERENCES - SECTION 1
Oglesby, Sabert, Jr.  Opening Remarks, EPA/Southern Research
Institute Symposium on Electrostatic Precipitators for the
Control of Fine Particles.   EPA-650/2-75-016,  Pensacola
Beach, Florida, September 30 - October 2, 1974.
                          1-5

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                          SECTION 2




          CONTROL SYSTEMS:  PARAMETERS AND CORRELATIONS





2.1  EMISSION SOURCES, CHARACTERISTICS, AND CONTROL SYSTEMS




     Following is a brief discussion of the processes covered  in




this report, their particulate emission characteristics, quan-




tities of emissions produced, and the types of conventional con-




trol devices used in each process.




2.1.1  The Kraft Pulping Process




     A schematic diagram of the kraft  (sulfate) pulping process




is presented in Figure 2-1.  The unit operations discussed in




this report are limited to recovery furnaces, smelt dissolving




tanks, and lime kilns.  Although not shown in Figure 2-1, the




power boiler is also considered an emission source if it is




fueled (or partially fueled) by wood bark, chips, or coal  (re-




ferred to in this report as a "bark/fossil-fuel" boiler).




     Pulping is the conversion of fibrous raw materials such as



wood, cotton, or recycled paper into a material suitable for use




in paper, paperboard, or building materials.  The principal




source of fibers is wood.  In the process, wood chips are cooked




(digested) at an elevated temperature and pressure in "white




liquor,"  a water solution of sodium sulfide  (Na_S) and sodium




hydroxide (NaOH).   The white liquor chemically dissolves lignin




(the material that bonds the cellulose fibers together) from the





                                2-1

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                             Wood Chip*
                   Steam
                                                Wh;»e L'auor (NaOH
§
O"


_i
u
O

CO


?
o
  Evaporator

  Gases








5
o
0
Q.
O
LLJ
"o.
'^
3

^





Weak
Block LJQU
S'eam
^~-

                               Digester
                                     Gases
                               Blow Tank
elief
4 Puip
t
Pressing
ond Drying
I


i
Vent
Gases
t
Knorter and
Washers











                                                  Causticizer

                                                  Tank
                                                   Settling


                                                   Tank
                                                    Filter
                              Fuel
                                                 Mud

                                                 Calcium

                                                 Carbonate
                                                                Kiln


                                                                Gases
Figure  2-1.   Kraft  pulping process,
                         2-2

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wood.  The remaining cellulose  (pulp) is filtered from the spent




cooling liquor, washed with water, and made into paper.




     The balance of the process is designed to recover both




cooking chemicals and heat.  Spent cooling liquor and the pulp




wash water are combined to form a weak black liquor, which is




concentrated to about 65 percent solids in multiple-effect evapo-




rators, then fired in a recovery furnace.  Two main types of




recovery furnace systems are used in the industry:  the direct-




contact evaporator system and the newer indirect-contact or  "low




odor" system.  To minimize total reduced sulfur  (TRS) emissions




from the conventional direct-contact system, the concentrated




black liquor must be oxidated before it is combusted in the




recovery furnace.  Combustion of the wood lignin dissolved in the




black liquor provides heat for generating process steam and




converting sodium sulfate  (Na_S04) to sodium sulfide  (Na^S).  To




make up for chemicals lost in the operating cycle, salt cake




(sodium sulfate)  is usually added to the concentrated black




liquor before it is sprayed into the furnace.




     The smelt, consisting of sodium carbonate (Na_CO-J and




sodium sulfide, is dissolved in water to form green liquor, which




is transferred to a causticizing tank, where quicklime (CaO)  is




added to convert the sodium carbonate to sodium hydroxide.




Formation of the sodium hydroxide completes the regeneration of




white liquor, which is returned to the digester.   A calcium




carbonate mud precipitates from the causticizing tank and is




calcined in a kiln to regenerate quicklime.  The condensate
                                2-3

-------
streams from the digester system and multiple-effect evaporator



system usually contain dissolved TRS gases.   These gases may be



removed with a condensate stripping system,  using either air or



steam in a stripping column,  before these streams are discharged



to the atmosphere.



Recovery Furnaces--



     In the recovery furnace, concentrated black liquor is




burned to produce a smelt of  sodium carbonate and sodium sulfide,



which is used to reconstitute cooking liquor.  Steam is a byprod-



uct of this operation.  As shown in Figure 2-2,  the furnace



consists of a combustion chamber and heat recovery equipment



(located directly above).  The rising flue gases pass through a



superheater section, the boiler tube bank, and an economizer



section before exiting to the contact evaporator unit.



     One of the two main types of recovery furnace systems used



in the industry incorporates  a direct-contact evaporator in the



final stage of black liquor evaporation; it is called a conven-



tional or direct-contact system.   (See Figure 2-3).  The other



main type is an indirect-contact, direct-fired,  or "low odor"



system.   (See Figure 2-4).  About 75 percent of the new furnaces



installed in the past 5 years are of this latter design.



Smelt Dissolving Tanks—



     The smelt dissolving tank is a large vessel  (3000 to 5000



ft ) located below the recovery furnace.  A molten mixture,



comprised primarily of sodium sulfide and sodium carbonate



(smelt), is removed continuously removed from the floor of the
                               2-4

-------
                 BABCOCK & WILCOX
                          Steam
COMBUSTION ENGINEERING
          4 Steam
               LEGEND

               1 . Furnace
               2. Smelt Spouts
               3. Block Liquor
               4. Primary Air Supply
               5. Secondary  Air Sopoly
               6. Tertiary Air Supply
               7. Position of Char Bed Burner? for Oil or Gas
               8. Normal Configuration o' Char Bed
               8'. Same  at Lav.  Primary Air Flow  and Pressure
               9. Screen Tubes
              10. Superheater
              1 1 . Boiler Tube Bonk
              12. Exit  to Economizer
     s r
                   Section A - A
Figure  2-2.   Principal  design  of recovery  boiler  furnace.
                                          2-5

-------
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2-7

-------
recovery furnace.  Water is added to this molten mixture in the




smelt dissolving tank to produce green liquor.   This tank is an




open vessel equipped with an agitator to assist dissolution and




a steam or liquid shatterjet system to break up the smelt stream




before it enters solution.   Entrained particulates are emitted




with large volumes of steam as the molten smelt and water mix.




The smelt dissolving tank is one of the main sources of partic-




ulate matter in a kraft pulp mill.




Lime Kilns--




     The lime kiln is an essential element of the closed-loop




system that converts the green liquor solution of sodium carbon-




ate and sodium sulfide to white liquor.  In the kiln the lime




mud (calcium carbonate that precipitates from the causticizer)




is calcined to produce calcium oxide  (quicklime, CaO) for re-




causticizing the green liquor.  The lime sludge typically enters




as a slurry with 55 to 60 percent solids.




     The kraft pulping industry generally uses large rotary




kilns capable of producing 40 to 400 tons/day of quicklime.




Fluidized-bed calciners are being used at four pulp mills, but




their current production rate is less than 150 tons/day and




accounts for only about 1 percent of the total quicklime produced




in the kraft industry.




     The rotary kiln turns at low speeds, causing the lime to




proceed downward toward the high-temperature zone  (1800° to




2000°F), which is sustained by combustion of natural gas or fuel




oil.  The lime mud dries as it moves along  (often aided by
                               2-8

-------
chains).  Baffles in the upper section of the kiln are sometimes


used to provide better contact with the hot gases.  Near the


lower end of the kiln, the lime agglomerates into small pellets,


and finally is calcined to calcium oxide in the high-temperature


zone near the burner.


     These lime kilns differ from those used in the lime manufac-


turing industry in that the calcium carbonate is generally fed


as a mud  (sludge)  containing 40 to 45 percent water instead of


as a solid (limestone).  This sludge contains a small percentage


of sodium sulfide, which affects the size distribution and


composition of the particulate in the exhaust gases.  The lime-


stone used in the lime industry does not contain sodium sulfide.


Bark/Fossil-Fuel Power Boilers--


     Based on 1972 figures compiled by the American Paper Insti-


tute, about 7 percent of the total energy requirement of the


pulp and paper industry is supplied by combustion of wastewood


and bark, an additional 33 percent is supplied by combustion of


its waste pulping liquors, and the remainder is provided by

                                         2
fossil fuels or by purchased electricity.


     According to a 1970 survey, 32 percent of the reporting


pulp and paper mills used bark plus other fuels in their power


boilers.  On a Btu basis, the average fuel utilization for a


group of 26 mills that reported emission data was as follows:


bark/wood, 48.5 percent; oil, 31.0 percent; coal, 11.3 percent/-


and gas, 9.2 percent.


     Wastewood- and bark-fired power boilers can burn wood alone
                                2-9

-------
or can be modified to burn other fuels on an auxiliary basis or




in combination.  In power boilers,  wastewood and bark are




burned on chain grates in a radiant Dutch-oven-type boiler or in




a horizontal, air-blown,  suspended  firing configuration in a




vertical Stirling boiler.  Wood handling systems (including




harranerrni 11 grinding to a  given particle size for suspended




firing), bottom and fly ash handling systems, and underfire and




overfire air controls must be provided.  Major fuel characteris-




tics affecting the design of wastewood-fired power boilers




include ash and moisture  content, particle size variations, and




fixed and volatile carbon content.




     The net heating value of most  wastewoods is about 7200 to




9000 Btu/lb of dry wood or 3600 to  5400 Btu/lb on an as-fired




basis.  The heating value of wastewoods tends to vary with wood




species.  The presence of extractive materials such as terpenes




and tall oils can substantially add to the energy content of the




wood.




2.1.2  Emission Characteristics - Kraft Pulping




     Characteristics of emissions from the various sources




discussed above are summarized in Tables 2-1 and 2-2.  The




average U.S. pulp mill emits about  5.5 Ib of particulate per ton




of air-dried pulp (ADP).   A well-controlled mill emits about 2.8




Ib/ton ADP.  Nationwide,  particulate emissions from kraft pulp




mills run about 89,000 tons/yr.  This amount would be reduced by




about 49 percent if the best available control systems were




applied to recovery furnaces, lime  kilns, and smelt dissolving






                               2-10

-------
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                                 2-11

-------
    Table 2-2.  CHARACTERISTICS  OF  PARTICULATE EMISSIONS
              FROM SELECTED U.S.  POWER BOILERS3
Number
of
boilers
18
2
2
16
2
2
2
3
2
Percent of fuel supplied
(3tu basis)
Coal
100
100
100
0
75
0
73
0
0
Oil
0
0
0
46
0
0
16
25
0
Gas
0
0
0
0
0
62
0
39
0
B/W"
0
0
0
54
25
38
11
36
100
Particulate
concentration
(uncontrol led ) ,
gr/ft3
1.87

4.89
3.47

2.30

1.88
1.40
E/W = bark and wastewood.
                             2-12

-------
tanks.




     Except for those from power boilers, particle size data are




generally lacking on emissions from kraft pulping operations.




Uncontrolled emissions from each process are discussed next.




Recovery Furnaces--




     The flue gas from black liquor recovery boilers contains




considerable particulate matter, which is formed by the release




of sodium from the smelt bed to the flue gas above it.  The




amount of sodium released appears to depend not on the sodium




content of the black liquor dry solids, but rather on partial




vapor pressures and diffusion conditions.  Characteristics of




emissions from conventional versus low order recovery furnaces




are discussed below.




     The primary difference in the low odor recovery furnace




operation as compared to the conventional process is the eli-




mination of direct contact between the concentrated black liquor




and the recovery boiler gases.  In general, the black liquor




leaving the evaporator at 45-50 percent solids is further con-




densed to 60-65 percent solids is a concentrator.  It is then



piped directly to the recovery boiler.




     Particulate emissions from a conventional recovery furnace




prior to application of a direct-contact evaporator or a control




device normally range from 8 to 12 gr/dscf (200 to 450 Ib/ton




ADP).  A direct-contact evaporator acts as a particulate control




device and reduces particulate emissions from a furnace system by




about 50 percent.   Particulate emissions from uncontrolled






                              2-13

-------
conventional recovery furnace systems currently in operation

average about 3.81 gr/dscf  versus about 7.93 gr/dscf for low

odor boilers.  Particulate matter emitted from the recovery

furnace consists of sodium sulfate and sodium carbonate and may

contain small amounts of sodium chloride.  Sodium chloride will

be present if the pulpwood has been stored in saline water or if

the makeup chemicals contain chloride impurities.

     Flue gas volume flow rates from recovery furnaces in general

can range from 32,000 to 400,000 scfm depending on pulp produc-

tion rate and volume of excess air used.  Temperatures of the

exiting gases (after economizer) fall in the range of 250° to

360°F for the conventional process versus 340°-450°F for the low

odor process.

     The conventional kraft recovery furnace is also one of the

largest emitters of reduced sulfur compounds in the pulping

process.  Concentrations of sulfur dioxide (S0_)  in the furnace

exhaust gases may be as high as 880 ppm.

Smelt Dissolving Tanks—

     Particulate consisting of dissolved and undissolved NaOH,

Na.CO,, and Na S is emitted from the dissolving tank with the

vented gases.  Uncontrolled emissions from a typical tank (1000

tons of pulp/day) may be as high as 380 Ib/h (8.0 Ib/ton ADP).

Exhaust gas flow rates may range from 11,000 to 22,000 scfm at

160° to 230°F.

Lime Kilns—

     Lime kiln particulate emissions consist principally of

sodium salts, calcium carbonate, and calcium oxide.  Because the
                              2-14

-------
sodium salt  (soda fume) emissions result primarily from sodium




compounds that are retained in the mud because of inefficient or




incomplete washing, particulate emissions are affected by the




efficiency of the mud washing system  (higher than normal sodium




levels in mud result in higher particulate emissions).   The




calcium particles result from entrainment; thus, emissions are




affected by the gas velocity and turbulence in the kiln.  Uncon-




trolled particulate emissions from a typical lime kiln can range




from 3 to 15 gr/scf, with exhaust volumes of 15,000 to 66,000




scfm.  Gas temperatures are usually about 400° to 500°F.  The




dust losses constitute about 1 to 5 percent of the total dry




solids load to the kiln.




     The rolling and tumbling of the lime in the rotary kiln and




the vaporization of sodium compounds  (carried into the kiln with




the lime mud) in the high-temperature zone and their later con-




densation are responsible for formation of most of the partic-




ulate matter in the kiln exhaust gases.  In addition to being an




air pollution problem, these emissions constitute a loss of




usable chemicals.




     The lime dust, made up of particles ranging from 1 to over




100 ym in diameter, is removed from the exhaust gas quite easily,




The soda fume consists of very small particles (most less than




1 ym in diameter) and is very difficult to remove.




Bark/Fossil-fuel Boilers--




     The major potential air pollutant from wood-fired power




boilers in the pulp and paper industry is particulate matter,






                              2-15

-------
which can result either from inorganic ash in the wood or from




incomplete combustion.




     Particulate emissions from wastewood combustion vary with




ash content and particle size of the material being  burned.   The




ash content can vary from less than 1 to 20 percent  by weight on




an as-fired basis.   The sizes and shapes of the wood particles




being burned can influence the design of grating systems, the




kind of firing, and the relative distribution of underfire and




overfire air in the furnace.  Furnace fouling often  occurs when




bark is fired,  especially when it is fired with other fuels.




Small amounts of minerals that are gathered in the fuel while it




is stored in sea water  or on ground can lower the ash softening




temperature so that it  becomes very sticky in the furnace and




cannot be easily removed.  The amount of particulate matter swept




from the combustion chamber is normally greater from horizontal




suspension firing units than from Dutch-oven-type units.




     Characteristic uncontrolled rates of particulate emission




from pulp mill power boilers were shown previously in Table 2-2.




Emissions from boilers  firing bark or a combination  of bark and




fossil fuels range from 1.4 to 3.5 gr/scf.  Typical  gas flow




rates in these types of boilers range from 19,000 to 200,000 scfm




at temperatures around  450°F.




     Particle size characteristics of emissions from bark/fossil-




fuel  boilers are presented in Table 2-3.  Bark that has been




soaked in salt water contains a much greater percentage of fine




particles than does freshwater bark  (60 to 70% particulate less
                              2-16

-------
    Table  2-3.
           TYPICAL  PARTICLE  SIZE  DISTRIBUTION  OF FLY ASH
             FROH BARK/FOSSIL-FUEL  BOILERS3
A.
Boiler fired with 100% bark
Particle size range,
;jm
<5
5-10
10 - 20
20 - 50
50 - 104
104 - 147
147 - 175
175 - 590
-590
Total
Other0
Percentage by weight
Flue gas
19.76
11.56
8.67
4. 82
3.37
16.24
3.65
17. 09
12.77
97. 93
2.07
Stack gas after cyclone
38.93
16.57
13.25
8.28
5.80
9.05
1.54
2.71
1.25
97. 38
2.62
B.
 Boiler fired with 401 bark - 60% coal
Particle size range,
;jm
+ 60
40-60
30-40
20-30
15-20
10-15
7.5-10
5. 0-7.5
3.5-5.0
2. 5-3.5
1.5-2.5
-1.5
Total %
% <10 u
% by
8.
7.
8.
13.
9.
14.
9.
10.
6.
5.
5.
4.
100.
31.
weight
5
5
0
0
0
0
0
0
5
0
0
5
0
0
  Particle size range by Banco method assuming a spherical particle
  and a specific gravity of 2.5.

  Average of two sampling runs.

  Due to handling loss.
                               2-17

-------
than 1.0 nn in diameter in high salt fuel).   Potential  gaseous
emissions a:   oxides of nitrogen,  oxides  of  sulfur,  and hydro-
carbons resulting from volatilization of  the bark.   The nitrogen
oxide emissions are generally lower than  those  from  fossil-fuel-
fired boilers because of the larger combustion  volumes  per  unit
amount of fuel burned, the normally higher excess  air  levels  (50
percent or more), and the higher fuel moisture  content  that
results in low flame temperatures  of 1800 to 2200°F.   Emissions
of SO  from bark-fired boilers generally  are low because the
sulfur content of bark is normally less  than 0.1 percent by
weight.  Emissions of terpenes, hydrocarbons, and  other volatile
organic constituents as a result of distillation and incomplete
combustion vary with wood species, furnace temperature, and
retention time.  The potential of  these  emissions  as air pollu-
tants has not been fully described.
2.1.3  Control Methods - Kraft Pulping
     The methods of emission control used at kraft pulp mills are
presented in the following paragraphs.
Recovery Furnaces--
     Nearly all recovery furnaces  are equipped  with electrostatic
precipitators for primary particulate control.   The  degree  of
control provided, however, varies  among  the  individual units.
Design efficiencies range from about 90  percent on older precipi-
tators to above 99.5 percent on recent installations.   The  lower
efficiencies on older units were established by balancing the
value of the recovered soda ash to the capital  outlay and oper-
ating expenses of the ESP.
                             2-18

-------
     Until recently, almost all recovery furnace systems incorpo-




rated a direct-contact evaporator.  Although the purpose of the




evaporator is to concentrate black liquor, it also scrubs partic-




ulate matter from the gas stream.  Depending on the type of




direct-contact evaporator used, it can remove up to 50 percent of




the particulate.




     Most mills use direct-contact evaporators of the cascade




type.  The furnace gases pass over a trough filled with black




liquor, which is scooped up by a rotating paddle wheel and then




cascaded through the gas stream.  Some mills use cyclones or




Venturis as the direct-contact evaporator.  In these installa-




tions the black liquor serves as the particulate scrubbing




liquid.  Sometimes two Venturis are used in series to increase




particulate collection, precluding the need for an electrostatic




precipitator.




     On some recovery furnaces, scrubbers have been installed




downstream from the precipitators.  'In the United States this




practice has been confined to upgrading of existing units.




     No applications of fabric filtration have been reported for




particulate emission control on recovery furnaces.  Because the




emitted matter is sticky, the filter bags would quickly become




blinded.  Mechanical dust collectors are also unsuitable for this




application because of the small particle size of the particulate.




     Information on Research Cottrell precipitators on kraft pulp




mill recovery boilers is presented in Appendix A-l.
                             2-19

-------
Smelt Dissolving Tanks--




     The gases from most smelt dissolving  tanks  are  vented




through mist eliminator pads with fine wire  mesh screens about 1




ft thick.  Mist eliminator pads are basically low-energy scrubbers




with collection efficiencies of about 80 percent.  Droplets




condensing from the gas collect on the screen and  are back-




flushed with  water sprays to the dissolving tank.   Several




dissolving tanks are equipped with more efficient  water  scrubbers,




such as low-pressure drop Venturis (6 to 8 in. of  water),  packed




towers, and cyclones with water sprays. Efficiencies of these




systems run about 95 percent.  A few mills combine the dissolving




tank gases with the recovery furnace gases and send  both streams




to an electrostatic precipitator.




Lime Kilns--




     The major ways of controlling particulate emissions from




lime kiln and fluidized-bed calciner exhaust gases are liquid




scrubbing (using either an impingement or  a venturi-type scrub-




ber) and recently, electrostatic precipitation.   Scrubbing




devices are usually located after a mechanical cyclone collector.




     Most lime kilns at kraft pulping plants are controlled with




venturi scrubbers with pressure drops ranging from 10 to 25 in.




H_0.  These systems provide collection efficiencies  of up to




about 99 percent.  A few kilns are controlled by impingement




scrubbers with wetted baffles and water sprays.   These scrubbers




have pressure drops of 5 to 6 in. HO and  provide collection




efficiencies of only about 90 percent.
                              2-20

-------
     Some kilns in Sweden are controlled by electrostatic pre-




cipitators.  Design efficiencies are about 99 percent.  One U.S.




mill has a retrofitted precipitator serving three kilns.




     Fabric filtration is not used as a control method for lime




kiln emissions because of the moisture content (25 to 35%) of the




exhaust gases.




Bark/Fossil-fuel Boilers--




     Control of particulate emissions from wood and bark/fossil-




fuel boilers normally is not as complex as control of emissions




from other processes within the pulp and paper industry.  The




problems and solutions are similar to those in conventional




boilers.




     The particulates from bark firing are often large,  5 to 10




ym or greter.  Because their specific gravity is usually low,




the use of mechanical cyclone collectors is not always effective.




Electrostatic precipitation of the fly ash is difficult  because




the high carbon content can cause low particle resistivity.




Minerals in the bark can cause abrasion in the collecting equip-




ment and ducts and resultant rapid metal wear.  More complete




analysis and classification of the chemical composition  and




physical size characteristics of particulate matter emitted




from bark-fired power boilers are needed.




     Electrostatic precipitators have been installed on  only a




few bark/fossil fuel fired boilers but have shown collection




efficiencies as high as 99.9 percent, (bark/coal fired boiler).




Cyclone collectors offer less efficient, but also less expensive,
                              2-21

-------
control for bark/fossil fuel boilers, and wet scrubbers or fabric



filters (which are effective for removal of particles below 5 urn)



offer an alternative to electrostatic precipitation.



     Granular bed scrubbers have also reportedly been used suc-



cessfully on a number of non-salt hogged fuel boilers.  However,



efficiency of the granular bed scrubbers falls off rapidly for



particles less than about 2 micrometers in diameter.  The Simpson



Timber Co. in Shelton, Washington rejected the granular bed



scrubber for use in controlling salt laden particulate from its



hogged fuel boilers because the scrubber would not remove the



blue haze caused by the primarily sub-micron salt particles.



     Since the granular bed scrubber is not an efficient collect-



or of fine particles, and has not been fully developed, a detailed



discussion of this device is not included in this report.



     Two pulp mills in the State of Washington use fabric filtra-



tion systems to control emissions from their power boilers.  Both



fire 100 percent bark and wastewood.



     The Simpson Timber Company in Shelton u as two fabric fil-



ters to reduce particulate emissions from their two power boilers.



Both are equipped with Teflon B-coated fiberglass bags.  The



units handle 100,000 and 130,000 acfm at about 500°F.  Both



collectors are preceded by mechanical collectors and were; in-



stalled to remove submicron NaCl particles from the exhaust gases



because the plant had experienced opacity problems with the



plumes from the power boiler stacks.  The air-to-cloth ratio



(A/C) is 4.5/1; the pressure drop is about 9 in. H^O.  The






                              2-22

-------
collectors are cleaned by pulse-air action, and operating exper-



ience is described by plant personnel as reasonably good in the



2 years since installation.



     The Long Lake Lumber Company in Spokane is the other pulp



mill using fabric filtration for power boiler emission control.



The fabric filter cleans approximately 17,200 acfm of effluent at



400°F and is equipped with Nomex bags that are cleaned by the



pulse-jet method.  A/C ratio is 4.0/1.  This collector has



reportedly been operating well for 3 years at a collection



efficiency of 99.7 percent.



     A Georgia-Pacific mill in Bellingham, Washington, has



recently contracted Standard Havens to install a 180,000-acfm



fabric filter to control particulate emissions from its four



bark-fired power boilers.  The unit will reportedly operate at a



net A/C ratio of 4.0/1 and a temperature of about 440°F.  It will



be outfitted with Teflon-coated fiberglass bags.  Georgia-Pacific



selected a fabric filtration rather than a dry gravel bed system



and venturi scrubber because they believe it to be the most



reliable and proven means of control.



     Two recent bark/oil-fired boilers equipped with venturi



scrubbers are Crown Zellerbach's Port Townsend and Port Angeles



plants near Seattle.  The Port Townsend plant has a salt emissions



problem because it fires sea-soaked bark; the Port Angeles plant



does not.  Both scrubbers are located downstream from a multi-




clone collector.  The Port Townsend scrubber operates at pressure



drops ranging from 15 to 20 in. HO, and outlet emissions have







                              2-23

-------
been tested at 0.07 to 0.18 gr/dscf depending on the salt content


of the bark.  Sodium chloride accounts for 26 to 70 percent of


total emissions.   The Port Angeles scrubber operates at pressure


drops from 8 to 10 in. H^O and outlet emissions have been measured


at 0.022 gr/dscf.   Thus,  the Port Angeles scrubber achieves a


lower emission rate at a  lower pressure drop than the Port Town-


send scrubber.  Opacity of the Port Angeles stack also is very


low.  These differences in operation can be attributed in large


part to the salt content  of the hogged fuel burned at the Port


Townsend plant, which cannot meet the 0.10 gr/dscf particulate


emission regulation when  the salt content of the fuel is greater


than 1 percent.


     A listing of  bark/fossil-fuel fired boilers from the National


Emission Data System  (NEDS) is presented in Table A.1-2, Appendix


A.  A number of particulate scrubbers operating on bark/fossil-


fuel boilers are summarized in Table A.1-3, Appendix A-l.


2.1.4  Crushed Stone Processing


     The conversion of naturally occurring minerals into crushed


stone products involves a series of interrelated physical opera-


tions.  Quarrying, transporting, crushing, size classification,


and drying are common to  almost all methods of mineral produc-


tion.  Particulate air pollution may result from any or all of


these operations.   The dust emitted is usually a heavy partic-

                                      4
ulate released at  ambient temperature.


     The initial step in  processing of crushed stone occurs at


the quarry site.   Blast holes are drilled vertically into the


exposed stone faces and charged with explosives; the rock is then


                              2-24

-------
blasted out of its deposit.  If secondary breakage is required,




"drop ball" cranes are normally used.  Oversize rock may also be




reblasted.  The broken rock is transported by 35- to 50-ton




trucks from the quarry pit to the primary crusher, which is often




in or near the quarry.  When portable plants are located in the




quarry itself, material can be fed directly to the primary




crusher by a power shovel.




     Crushing plant operations common to most crushed stone




installations are primary crushing, scalping, secondary crushing,




tertiary or finishing crushing, final screening, conveying,




storage and shipping, and in some instances, washing.  Depending




on the purpose of the plant and the kind of rock processed, all




or only a few of these operations take place.




     As illustrated in the flowsheet in Figure 2-5, broken rock




obtained from the quarry is dumped into a hoppered feeder,




usually a vibrating grizzly type, and fed to the primary crusher




for initial reduction.  Jaw or gyratory crushers are normally




used,  although impact crushers are gaining favor for crushing




low-abrasion rock  (e.g., limestone) and when high reduction




ratios are desired.  The crusher product  (normally in pieces 3 to




12 in. in size) and the "grizzly throughs" are discharged onto a




belt conveyor and transported to a surge pile or silo for tem-




porary storage.




     The material is then reclaimed, usually by a series of




vibrating feeders under the surge pile, and conveyed to a scalp-




ing screen, which separates the process flow into three fractions
                               2-25

-------
                                                                                         c
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                                                                                         a

                                                                                         cu
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                                        2-26

-------
 (oversize, undersize, and "throughs") prior to secondary crush-




 ing.  The oversize is discharged to the secondary crusher for




 further reduction.  The undersize, which requires no further




 reduction at this stage, normally bypasses the secondary crusher,



 thus reducing its crushing load.  The "throughs," which contain




 unwanted fines and screenings, are usually removed from the



 process flow and stockpiled as crusher-run material.  Gyratory or




 cone crushers are the most commonly used for secondary crushing,




 although impact crushers are used at some installations.



     At a typical operation the product from the secondary




 crushing stage (usually 1 in. or less in size) is transported to




 a secondary screen for further sizing.  Sized material from this



 screen is conveyed or discharged directly to tertiary crushing,




which takes place on cone crushers or hammermills.  The product




 from the tertiary crushers is shuttled back to the secondary




 screen, forming a closed circuit with a fixed top size.  The



 throughs from this screen are discharged to a conveyor and




elevated to a screen house or tower containing multiple-screen




 lines for final sizing.  At this point,  end products of desired




 gradation are chuted directly to finished product bins or trans-




ported by conveyors or trucks to stockpiles in open areas.



     Sometimes stone washing is required to meet particular end




product specifications or demands, such as those for concrete




aggregate.  Washing plants consist of a number of fine mesh



 screens onto which the material falls and is sprayed with a heavy




water-spray.  Unwanted fines are usually discharged to a settling




pond.




                               2-27

-------
2.1.5  Emissions Characteristics - Crushed Stone




     Particulates emanate from many sources (both process and




fugitive) in a quarry and crushed stone plant.   Process sources




include drilling, crushing and grinding, conveying and elevating




(transfer points), stockpiling  (the actual operation itself),




and screening.  Fugitive emissions are generated by blasting,




loading, hauling, stockpiling (e.g.,  free fall), and also are




windblown from roads, plant yards, and stockpiles.  No precise




estimate of fugitive emissions has been made.




     Quantitative data on emissions from these  sources are




practically nonexistent.  The few data available are conflicting




and,  in some cases  (such as when material balances are used)




without basis.  Examples of the ranges in the  available emissions




data and corresponding emission factors are presented in Table




2-4.




     Examination of the data in Table 2-4 leads to several




conclusions.  First, emission factors do not take into account




the kind of rock, which is a very important parameter.  Second,




in most cases reported emissions are considerably higher than




the emission factors.  Third, reported emission values are




inconsistent with the operation performed and  the corresponding




emission factor.  For example, the emission factor for secondary




crushing and screening is three times that for primary crushing,




but reported emissions from primary crushing are much higher




than those for secondary.




     Factors affecting emissions that are common to most crushed
                               2-28

-------
Table 2-4.   REPORTED UNCONTROLLED EMISSIONS  VERSUS
                   EMISSION FACTORS^
Operation
Primary crushing
Secondary crushing and
screening
Tertiary crushing and
screening
Recrushing and
screening
Screening, conveying,
and handling
Reported emissions,
Ib/ton
4.9 - 120
0.26 - 13.7

3.6 - 18.2

0.6 - 7. 97

1.4 - 125
Emission factors,
Ib/ton
0.5
1.5

6. 0

5. 0

2. 0
                          2-29

-------
stone operations include moisture content of the rock,  the kind




and amount of rock processed,  the equipment and operating prac-




tices, and a variety of geographical and seasonal factors..




These factors apply to both fugitive and process sources asso-




ciated with either quarrying or plant operations.




     .Minimal data are available to define the particle  size




characteristics of dust generated in stone processing operations.




It is usually a fairly coarse particulate containing some mois-




ture.  Particle size depends on the kind of rock, the processing




equipment, and the stage of processing.   Figure 2-6 presents




particle size data on emissions from a jaw crusher and  a conveyor/




screening operation.  Less than 10 percent of the particles




emitted from the crusher are smaller than 10 pm, whereas 50




percent of those conveyor/screening operations are below 10 urn.




Drilling  (Quarrying)—




     Emissions from drilling operations  result primarily from




air flushing to remove cuttings and dust from the bottom of the




hole.  Putting compressed air down the hollow drill center




forces cuttings and dust up and out the  annular space between




the hole wall and drill.  Factors affecting the level of uncon-




trolled emissions include the kind of rock, the moisture content




of the rock, the type of drill, the diameter of the hole, and the




penetration rate.




Crushing—




     Generation of particulate emissions is inherent in the




crushing process.  Most apparent at crusher feed and discharge







                              2-30

-------
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                                                                   en
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          2-31

-------
point, the emissions are influenced by various  factors,  including




the moisture content of the rock,  the  kind  of rock,  the  pro-




cesses, and the type of crusher.




     The crushing mechanism (i.e.  compression or impact)  is  the




most important element influencing emissions from crushing




equipment.  It has a substantial  effect on  the  size  reduction




achieved; the particle size distribution of the product,  es-




pecially the proportion of fines  produced;  and  the amount of




mechanically induced energy that  is imparted to the  fines.




     Impact crushers produce a larger  proportion of  fines than




compression crushers.  They also  impart more velocity to the




fines as a result of the fan-like  action produced by the spinning




hammers.  Hence, impact crushers  generate more  uncontrolled




particulate emissions per ton of  stone processed than any other




crusher type.




     Uncontrolled emissions from  compression crushers (jaw,




gyratory, cone, and roll crushers) closely  parallel  the  reduction




stage to which they are applied;  the greater the reduction,  the




higher the emissions.  Primary jaw crushers probably produce  more




dust than comparable gyratories because of  the  bellows effect of




the jaw and because gyratory crushers  are usually choke-fed,




which minimizes the open spaces from which  dust can be emitted..




In subsequent reduction stages, cone crushers produce more fines




as a result of attrition, and consequently  generate more dust.




Screening—



     Dust is emitted from screening operations  as a result of
                              2-32

-------
the agitation of dry stone.  The level of uncontrolled emissions




is dependent on the particle size of the material screened, the




amount of mechanically induced energy transmitted, and other




factors already discussed.




     Generally, the screening of fines (less than 1/8 in.) pro-




duces more emissions than the screening of coarse sizes.  Screens




agitated at large amplitudes and high frequency emit more dust




that those operated at small amplitudes and low frequencies.




Conveying (Transfer Points)--




     Particulates may be emitted from any and all materials




handling and transfer operations.  As with screening, the level




of uncontrolled emissions is dependent on the size of the mate-




rial and how much it is agitated.  Perhaps the worst case




occurs at conveyor belt transfer points,  where material is




discharged from the conveyor at the head pulley or received at




the tail pulley.  The quantity of emissions depends on the con-




veyor belt speed and the free-fall distance between transfer




points.




Storage Bins--




     The transfer of final stone product to storage bins by




conveyor belt or chute generates dust emissions similar to those




from other transfer operations.   Significant particulate emis-




sions also may evolve from loadout of the stored material into




open dump trucks.   Again,  the amount of dust generated depends




on the moisture content of the stone and the free-fall distance.
                              2-33

-------
2.1.6  Control Methods - Crushed Stone Operations

     Because a typical stone crushing plant contains a multi-

plicity of dust-producing points, effective emission control is a

complex and difficult problem.   Methods for control of plant-

generated emissions include wet scrubbers,  wet dust suppression,

dry collection, and a combination of both wet suppression arid dry

collection.  In wet dust suppression, moisture is introduced into

the material flow,  causing fine particulate matter to be confined

and remain with the material flow rather than to become airborne.

Dry collection involves hooding and enclosing dust-producing

points and exhausting emissions to a collection device.  Combina-

tion systems (Figure 2-7) utilize both methods at different

stages throughout a stone processing plant.  The use of enclosed

structures to house process equipment is also an effective control

technique.

     In a wet dust-suppression system, dust emissions are con-

trolled by spraying moisture (water or water plus a wetting

agent) at critical  dust-producing points in the process flow.

This causes dust particles to adhere to larger stone surfaces or

to form agglomerates too heavy to become, or remain, airborne.

Thus, the objective of wet dust suppression is not to fog an

emission source with a fine mist to capture and remove emitted

particulates,  but rather to prevent their emission by keeping the

material moist at all process stages.

     Small quantities of specially formulated wetting agents or

surfactants are blended with water to reduce its surface tension

and consequently improve its wetting efficiency so that dust

particles may be suppressed with a minimum of added moisture.
                               2-34

-------
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     The dilution of such an agent in minute quantities in water




 (1 part wetting agent to 1000 parts water)  is reported to make




dust control practical throughout an entire crushed stone plant




with as little as 1/2 to 1 percent total added moisture per ton




of stone processed.




     A typical wet dust-suppression system illustrated in Figure




2-8, contains several basic components and features,  including




 (1) a dust control agent (compound M-R), (2)  proportioning




equipment, (3) a distribution system, and (4)  control actuators.




A proportioner and pump are necessary to proportion the wetting




agent and water at the desired ratio and to provide the moisture




in sufficient quantity and at adequate pressure to meet the




demands of the overall system.




     Distribution is accomplished by spray headers fitted with




pressure spray nozzles.  Headers are used to apply the dust-




suppressant mixture  at each treatment point at the rate and spray




configuration required to effect dust control.




     Particulate emissions generated at plant process facilities



 (crushers, screens,  conveyor transfer points, and bins) may also




be controlled by capturing and exhausting emissions to a dry




collection device.  Depending on the physical layout of the




plant, emission sources may be manifolded to a single centrally




located collector or to a number of strategically placed units.




Collection systems consist of an exhaust system with hoods and




enclosures to confine and capture emissions and ducting and fans
                             2-36

-------
Truck Dump
and Feeder
                     Bog Collector
V
                  Primary
                  Crusher    Secondary
                    0      Crusher
           Bin and Truck
           Loadinc Station
                        Succressior
                        Collecrior
                                                             Tertiary
                                                             Crusher
 Figure  2-8.   Wet  dust-suppression  systems.
                              2-37

-------
to convey the captured emissions to a collection device where




particulates are removed from the air stream before it is ex-




hausted to the atmosphere.




     The most commonly used dust-collection device in the crushed




stone industry is the fabric filter  (or baghouse).  In most




crushing plant applications, mechanical-shaker collectors (which




require periodic shutdown for cleaning after 4 or 5 hours of




operation) are used.   These units are normally equipped with




cotton sateen bags and operated at an A/C ratio of 2 or 3 to 1.




A cleaning cycle, normally  actuated automatically when the




exhaust fan is turned off,  usually requires only 2 or 3 minutes




of bag shaking.




     Fabric filters with continuous cleaning are used where it




may be impractical to turn  off the collector.  Compartmented




mechanical-shaker units may be used, but jet-pulse units are




preferred.  Jet-pulse units normally have wool or synthetic




felted bags as the filtering medium and can be operated at a




higher filtering ratio  (as  high as 6 or 10:1).  Greater than 99




percent efficiency can be attained with either type fabric




filter, even on submicron particle sizes.  Outlet grain loadings




recorded during EPA emission tests at several crushed stone




facilities processing various kinds of rock seldom exceeded




0.01 gr/dscf.5




     Other collection devices reportedly used in the industry




include cyclones and low-energy scrubbers.  Although these




collectors may provide high efficiencies  (95 to 99%) on coarse




particles  (40 um and larger), their efficiencies are poor  (less




                               2-38

-------
than 85%) on medium and fine particles (20 \im and smaller).




Although high-energy scrubbers and electrostatic precipitators




could conceivably achieve results similar to those of a fabric




filter, these methods are not currently used in the industry.




     Dust control at portable crushed stone plants is considered




by some industry spokesmen to be extremely difficult; however,




the successful application of a wet dust-suppression system has




been reported.   Furthermore, trailer-mounted, portable baghouse




units are commercially available and have been used to control




emissions from portable asphalt concrete batch plants.  Although




application of dry collection systems at portable crushed stone




plants is not widespread,  portable plant equipment manufacturers




have indicated unofficially that this control option is indeed




feasible and that the required hoods, enclosures, and ductwork




could be integrated into the design of portable plant components.




At least one manufacturer has drafted a proposal for such an




installation.




Drilling--




     The two control methods available for controlling particulate




emissions from drilling operations are water injection and




aspiration to a control device.




     Water injection is a wet drilling technique in which water




or water plus a wetting agent or surfactant, usually a liquid




detergent, is injected into the compressed air stream used to




flush the drill cuttings from the hole.  The injection of the




fluid into the air stream produces a mist, which dampens the






                              2-39

-------
stone particles and causes them to agglomerate.   As  the particles




are blown from the hole,  they drop as damp pellets at  the drill




collar rather than becoming airborne.




     Dry collection systems can also be used to  control emissions




from the drilling process.  A shroud or hood encircles the drill




rod at the hole collar.   Emissions are captured  under  vacuum and




vented through a flexible duct to a control device  for collection.




The device is often mounted on the drilling rig.  Various devices




are available, and their efficiencies vary.  Cyclones  or fabric




filters preceded by a settling chamber are the most  common.  Air




volumes required for effective control range from 500  to 1500




cfm, depending on the kind of rock, the hole size,  and the




penetration rate.




Crushing—




     Wet suppression techniques are currently used  on  most




crushers, with the exception of limestone crushers.   Application




of treated water at the feed point of the crusher has  been proven



effective in minimizing particulate emissions.




     When dry collection systems are used, the upper portion of




the crusher should be enclosed as completely as possible and




exhausted according to the criterion established for transfer




points.  The crusher discharge/transfer belt interface also




should be totally enclosed.  An example of this type of system




is shown in Figure 2-9.   The exhaust rate will vary considerably




with the type of crusher.  Exhaust volumes from impact crushers




or hammermills range from 4000 to 8000 cfm, whereas an exhaust






                               2-40

-------
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                                  2-41

-------
rate of 500 cfm/ft of discharge opening should be sufficient on




compression-type crushers.   In either case,  pickup should be




applied downstream of the crusher at a distance at least 3.5




times the width of the receiving conveyor.




     To achieve effective emission control,  ventilation should




be applied both at the upper portion (or feed) of the crusher




and at the point of transfer to the belt (or crusher discharge).




This would not apply to primary jaw or gyratory crushers because




operators must have ready access to dislodge large rocks that




sometimes become stuck in the crusher feed  opening.




Conveyor Transfer Points--




     Water spraying effectively controls the dust generated by




transferring crushed stone  between conveyors.   This method




cannot be used, however, when a dry product is needed at the




next step of the operation  or when there is a market for the




fines collected by a dry control system.




     The alternative method of control is complete enclosure of



the conveyor or the transfer point.  Complete enclosure of both




is impractical and rarely used.




     At belt-to-belt conveyor transfer points, hoods should be




designed to enclose both the head pulley of the upper belt and




the tail pulley of the lower belt as completely as possible.  By




careful design, the open area should be reduced to about 0.5




ft /ft of belt width.   Conveyor belt speed and free-fall




distance are factors that affect the air volume to be exhausted.
                              2-42

-------
Screening--


     Water sprays are used in most operations where wet or damp


stone can be tolerated in the rest of the process.  Water spray


bars or nozzles are normally located at the discharge point of


the conveyor, on the screen itself, and at the discharge points


of the screen.  This method has the following disadvantages:  wet


dust may bind on small screens, the water may retard later


processes or prevent the stone from meeting specifications if the


dust is not washed off.  The use of washing plants will overcome


most of these disadvantages.


     Effective dry control at screening operations normally re-


quires the use of several exhaust points.  A full-coverage hood


is often used to control emissions generated at screening sur-


faces.  Additional or alternative ventilation air may be required


at the screen feed and discharge ends.  Exhaust volume require-


ments vary with the surface area of the screen and the amount of


open area around the periphery of the enclosure.  A well-designed


enclosure will have a space of no more than 2 to 4 in. around the


periphery of the screen.


Storage Bins--


     Belt- or chute-to-bin transfer points differ from other


transfer points in that there is no open area downstream of the


transfer point.  Hence, emissions are emitted only at the loading


point.  The ventilation point is normally located at some point


remote from the loading point and exhausted at a minimum rate of

          2
200 cfm/ft  of open area.  Small fabric filter collectors (2000


to 6000 acfm) are then used to clean the dust-laden exhaust

                              2-43

-------
stream.  The fabric filter may also be used to collect dust




emitted from loadout operations beneath the storage bins.




Snorkel hoods, which consist of an annular space around the




opening of the discharge chutes, are an effective means of




minimizing particulate emissions that occur as trucks are being




loaded with stone product.




2.2  EVALUATION OF VARIOUS CONTROL ALTERNATIVES




     A number of factors that must be weighed in selection of a




control device for a specific process and plant are given in




Table 2-5.




     In terms of the technical competitiveness of the various




control devices under consideration, the processes often dictate




the selection of the control device.  For example when the revised




kraft pulp mill emission standards are implemented, it may




become necessary to develop hybrid systems either extending the




capability of the existing unit or adding other generic control




devices.  Especially with regard to bark boilers, the historical



use of mechanical collectors alone will no longer be adequate to




meet proposed regulations.  Increasing efficiency requirements




may cause a shift in the selection of control devices as well as




a move to industrial energy conservation.




2.3  ELECTROSTATIC PRECIPITATORS




2.3.1  System Design Parameters




     This section deals with the major parameters that must be




weighed in design of an electrostatic precipitator.  The process




applications under consideration are recovery furnaces and
                               2-44

-------
    Table 2-5.  FACTORS BEARING ON CONTROL DEVICE SELECTION
  Characteristics of
particles and gas stream
Facilities, costs, legal
         factors
Particles

 Electrical properties
  (precipitators only)
  Resistivity
  Dielectric constant

 Physical properties
  Surface properties
   abrasiveness
   porosity
  Density
  Shape
  Hygroscopic nature
  Adhesivity
  Cohesivity

 Particulate concentration

 Size distribution

Gas stream
 Flow rate
 Process
 Viscosity
 Chemical composition
 Acid constituents
 Alkaline constituents
 Sulfur oxide content
 Moisture content
 Plant facility

 Waste treatment
 Space restriction
 Product recovery
 Water availability

Co_s_t of control
 Engineering studies
 Hardware
 Auxiliary equipment
 Land
 Structures
 Installation
 Start-up
 Power
 Waste disposal or recycle
 Water
 Materials
 Gas conditioning
 Labor
 Maintenance
 Taxes
 Interest on borrowed capital
 Depreciation
 Insurance
 Return on investment

 Regulations
 Maximum particulate and SO,,
  emission rates allowed by
  Federal, state, and local laws
                              2-45

-------
bark/fossil-fuel boilers in the kraft pulp mill industry.   The

dust emitted includes sodium sulfate, sodium carbonate,  and

sodium chloride from recovery furnaces and carbon (char),  sand,

and fly ash from bark/fossil-fuel boilers.

     These industrial applications are essentially all retrofit

pollution control systems  (and therefore site-specific).   Varia-

tion in processes can cause wide differences in expected per-

formance.

     The design procedure is straightforward; given certain

input variables  (process application, process flow correlations

and parameters, and applicable particulate emission standard)

and applying experience and theory, one can develop a design

that meets the criteria for efficiency and cost.  This format is

illustrated in Table 2-6.

      Table 2-6.  PARAMETERS AFFECTING PRECIPITATOR DESIGN
 System input
Basic design
 parameters
Specific design
  parameters
 System output
Process appli-
 cation
Process condi-
 tions
Applicable
 erni ssion
 standard
Total acfm
Total col-
 lection area
Power
 density
Gas and dust
 characteristics
Precipitator
 capacity
Electrical/
 mechanical
Electrical
 energization
System perform-
 ance
Overall and
 fractional mass
 collection
 efficiency
Capital invest-
 ment
Annual cost
Basic Design Parameters--

     The objective here is to determine from the process applica-

tion, process conditions, and applicable emission regulations the

values for gas volumetric throughput  (acfm), total plate collection
                               2-46

-------
        2                              2
area  (ft ), and power density (watts/ft  of collecting surface)



These three parameters form the basis for precipitator design.



     The total gas volume is dictated by process and production



level.  Knowing the total acfm and the specific collection area


        2
(SCA, ft /1000 acfm) ,  one can determine the total area required



to comply with an emission regulation.  The equations for doing



so are given below.
               SCA =                                   (Eq
                             wk
                           i



where



     ~ = Overall mass collection efficiency, percent



     b = Slope of line (reference line slope = 0.5)



    w  = Modified migration velocity, ft/sec
     K.


    C  = Allowable outlet grain loading,  gr/dscf*



    C. = Inlet grain loading, gr/dscf*






     The proposed Federal standard for new recovery furnaces is



0.10 g/dscm**  of saltcake emissions and is equivalent to 0.04



gr/dscf.  Based on a typical inlet concentration of 3.8 gr/scf



for a conventional recovery furnace, this corresponds to a



required control efficiency of 98.95 percent. Where codes are



based on pounds of particulate emitted per air-dried ton of pulp,



the 0.04 standard may not be stringent enough for high product



processing levels.
 * dscf = dry standard cubic foot.

** dscm = dry standard cubic meter.

                              2-47

-------
     The presence of fines,  although representing  a small weight

fraction, may cause a visible plume.   Where "equivalent opacity"

is used as a standard, a visible plume may not be  acceptable.

     The following excerpt from rules and regulations for kraft

pulp mill applications in the Federal Register illustrates
                   Q
proposed standards.

     "The proposed standards would limit emissions of particulate
     matter from three affected facilities at kraft pulp mills.
     The limits are (1)  0.10 gram per dry standard cubic meter
     (g/dscn)  for recovery furnaces,  (2)  0.15 gram per kilogram
     of air-dried pulp (g/Kg ADP)  for smelt dissolving tanks,   (3)
     0.15 g/'dscm for lime kilns when burning natural gas and (4)
     0.30 g/dscm for lime kiln when burning oil.   Visible emis-
     sions from recovery furnaces would be limited to 35 percent
     opacity. "

     Migration velocity—The modified migration velocity is a

function of electrical energization of the precipitator and of

gas properties.  It is often conveniently linked with resistivity

level.   A representative range of migration velocity in the pulp

and paper industry is 0.21 to 0.31 ft/sec.  Because of the vari-

ation in the ash resistivity due to cyclic operation of the

pulping cycle a precipitator designed for recovery furnaces may

have an uncertainty of approximately 15 to 20 percent in pre-

cipitator migration velocity.  For example, in a precipitator

designed for 98 percent collection efficiency, the measured
                                               9
efficiency could vary from 97 to 98.40 percent.   A typical

migration velocity range in bark/fossil-fuel boiler applications

is 0.2  to 0.5 ft/sec.

     A  digression is in order at this point to clarify the usage

of w  (modified migration velocity) in contrast to the effective
                              2-48

-------
migration velocity w, which is used in the conventional Deutsch-

Anderson efficiency equation.  The effective migration velocity,

w, is a function of several factors, including precipitator

length, overall mass collection efficiency, and gas velocity.

The variation in w within a given precipitator is caused by

changing particle size distribution as precipitation proceeds in

the direction of gas flow.

     The modified migration velocity, w ,  as presented by Matts
                                       K
and Ohnfeldt   can be treated essentially as a constant for any

application.  It is, of course, strongly dependent upon the inlet

particle size distribution.

     Power input--The third basic design parameter is power

density required to establish the optimum voltage-current charac-

teristics of the corona, given the dust entering the precipita-

tor.   Power density is a function of electrical resistivity,

particle size characteristics and distribution, gas loading and

composition, gas temperature, and gas pressure.  It is often

conveniently linked with resistivity, such that for a moderate
                 g
resistivity of 10  ohm-cm the value will be approximately 2,5
        2
watts/ft .  For recovery furnaces a typical range of power input
                      2
is 1.1 to 1.5 watts/ft , as calculated from field operating data.
                                                          2
For bark boilers a range of power input is 1 to 3 watts/ft .

     Table 2-7 illustrates a general correlation between power

density and dust resistivity, based on typical values for fly

ash.
                              2-49

-------
               Table 2-7.   DESIGN POWER DENSITY
Resistivity, ohm-cm
lO4'7
107'8
109'10
1011
io12
>io13
Watts/ft
collecting
4.0
3.0
2.5
2.0
1.5
<1.0
2 of
plate






     Operating voltages from field data can range from 45 to 55



kV for 9-inch plate spacing.  Current densities,  also from field



data,  range from 0.02 to 0.05 mA/ft  for recovery furnace applica-



tions.  Field voltages and current densities for bark boilers



range from 40 to 45 kV and 0.02 to 0.06 mA/ft ,  respectively.



Thete values are not constant for each point in the precipitator.



At the inlet section where the dust loading is greatest, the



voltage-current characteristics will be significantly different



from those at the outlet.



     It appears that resistivity plays a significant role in



selection of w,  and power density, yet there is no precise or
              }C


universally applied method for predicting resistivity from the



material entering the furnace or process and the process condi-



tions .



Specific Design Parameters--



     Table 2-8 is a compilation of design parameters and input



variables grouped in logical categories.



     Precipitator Size—One of the first structural parameters




                               2-50

-------
    Table 2-3.  DESIGN PARAMFTERS  AND  DESIGN  CATEGORIES  F0"l
                   ELECTROSTATIC PRECIPITATORS
Dust composition -*•
     NaCl
     C (Char)
     Sand
     Fly ash
Precipitator capacity
     No.  precipitators
     No.  chambers (units) /precipitator
     No.  ducts/chamber (unit)
     Duct spacing
     Plate height
     Treatment length
     Section lengths and total no. of each (per precipitator)
     Collecting area
     No.  electrical sections parallel to gas flow  (per precipita-
      tor)
     No.  electrical sections across gas flow (per precipitator)
     No.  hoppers parallel to gas flow (per precipitator)
     No.  hoppers across gas flow  (per precipitator)
Rapping,  electrodes, etc.
     Type discharge electrode
     Length discharge electrode/vibrator or rapper
     Type discharge electrode/vibrator or rapper
     Type collecting electrode
     Area collecting electrode/rapper
     Type collecting electrode rapper
                              2-51

-------
Table 2-8 (continued!
Electrical energization (of each electrical section)
     Power density
     Length of collecting electrode/T-R
     Mode (switching)
     Corona power
     Current density
     Current/T-R set
                t_ed_ parameters
                                   Overall mass collection
                                     efficiency
                                   Fractional mass collection
                                    efficiency
     Gas flow
     Gas teroerature
     Gas (treatment)  velocity
     SCA
                                   Inlet grain loading
                                   Outlet grain loading
                              2-52

-------
to be determined is the width of the precipitator (s ) .  This

value is dependent on the total number of ducts as determined

from Equation 1.
     Total no. ducts = TYrvToTTpTs . ) ( P . H . )           (Eq' 2)

where

     acfm = total gas volumetric throughput, acfm

     T.V. = gas  (treatment) velocity, ft/s

     P.S. = plate spacing, ft

     P.H. = plate height, ft

     A practical approach from the standpoint of energization

and reliability is to limit the total number of ducts per chamber,

The number of chambers is determined by the total number of

ducts, which is determined from Equation  2 and the associated

criteria.  The total number of precipitators needed will depend

on the degree of reliability required, space limitations at the

plant site, and the relative ease with which the effluent gas

can be distributed to the precipitator (s ).

     The second general design equation provides a guide to the

length of the precipitator, which is dependent on treatment

velocity, plate spacing,  plate height, gas volumetric throughput,

and total collecting surface.                     (Eq. 3)

Treatment _
 length

                    Total collection surface
(No. pptrs.)(No. chambers/pptr.)(No. ducts/chamber)(P.H.)(2)
                              2-53

-------
The design treatment length will be determined by selection of an




integer value of standard section (field)  lengths that may be




offered by the precipitator manufacturer.   If it is found, for




example, that four fields are required,  two of one length and two




of another, structural considerations such as hopper spans may




determine the positioning of the fields  in the direction of gas




flow.




     Mechanical sections result from the chamber-wise and field-




wise sectionalization of an electrostatic  precipitator.  Hopper




selection is based on the size of the mechanical sections and the




predicted inlet grain loading.




     Treatment velocity (T.V.) is a function of dust resistivity.




In recovery furnace applications, the precipitator treatment




velocity ranges from 2 to 5 ft/s; in bark/fossil-fuel boiler




applications the range is 3.2 to 4.5 ft/s.  The lower velocity




should be considered when burning salt-water-soaked bark material.




In general, the less resistive the dust, the shorter can be the




treatment time.



     Plate spacing is more or less fixed by the precipitator




manufacturer, depending on his experience with the various




process applications and conditions, predicted velocity distri-




bution across the precipitator, and type of plate.  Plate spacing




usually ranges from 9 to 12 inches.




     In selecting plate height, the designer attempts to maintain




both the required treatment velocity and an adequate aspect
                              2-54

-------
ratio.  The aspect ratio is defined as the ratio of the length of

a precipitator to its height.  Historical data indicate that it

can vary from 0.75 to 1.5.   The practical limitations on plate

height imposed by structural stability requirements are obvious.

Each manufacturer limits the practical plate heights in accord-

ance with the overall design.

     The total number of ducts dictates the width of the pre-

cipitator.  The designer next requires some indication of the

system sectionalization, as indicated in Figure 2-10.  Chamber-

wise  (parallel) sectionalization is sectionalization across the

gas flow, whereas series sectionalization is in the direction of

aas flow.







•H





m
SERIES www
SECTIONALIZATION cQ m «

4
K K S
i U U 0
                                     3rd FIELD
                                     2nd FIELD
                                     1st FIELD
                    SERIES AND PARALLEL
                       SECTIONALIZATION
                            t
                                                      PARALLEL
                                                 SECTIONALIZATION
t
               (GAS FLOW  INDICATED BY ARROWS)


        Figure 2-10.   Sectionalizatior of a precipitator.

                              2-55

-------
     Discharge/collection electrodes--The geometry of the dis-


charge electrode  (fine,  barbed,  rigid,  etc.)  will determine


corona current-voltage characteristics.   The  smaller the wire or


the more pointed its surface,  the greater the value of corona


current for a given voltage.   Very fine or exotic wires, howevesr,


may have potential for breakage  and possible  dulling of spiked


points with time.


     The maximum value for length of standard 0.109-in.-diameter


discharge wire per vibrator is 3000 ft  in recovery furnace


precipitators and 3500 ft in bark boilers.  The area of collect-


ing surface per vibrator or rapper usually ranges from 2000 to

       2
2500 ft  in bark boiler precipitators.


     Baffles are used to provide stiffness for support of the


collecting plate and a region of low turbulence to minimize


reentrainment of dust, particularly during rapping.  Although a


variety of plates are commercially available, their functional


characteristics are not substantially different.


     V i b r a t o r s / r a p p e r s - - Th e air  vibrator imparts energy at high


frequency to the discharge electrodes and collecting plates.


The system is designed to create a vibration in the collecting


plates and discharge electrode wires to dislodge accumulations


of particles so that the plates  and wires are kept in optimum


operating condition.  A pressure setting of 35 to 40 psi on the


pneumatic vibrator is generally  adequate.  Rappers are occasion-


ally used on kraft pulp mill applications instead of vibrators


for cleaning wires.
                               2-56

-------
     Rappers can be pneumatic or electromagnetic.  Single-impact




 (magnetic-impulse, gravity-impact) rappers are often used.  The




rapping intensity is determined by the height of the rapper when




released from its elevated position and by the plunger weight.




The weight of the plunger may be from 8 to 32 Ib.  The frequency




of rapping is determined empirically by observing the values of




opacity and overall mass collection efficiency measured as the




intensity of rapping is varied.




     Electrical energization--The way in which a precipitator is




energized has a great effect on its performance.  Selection of




the energization system is probably as site-specific as it is




process-specific.  The chief considerations in both utility and




industrial applications are number and size of T-R sets,  the




number of electrical sections,  degree of high-tension sectionali-




zation, half wave - full wave  (HW-FW) operation, and changes in




voltage-current characteristics as precipitation proceeds in the




direction of gas flow.




     A mechanical section by definition may become an electrical




section (bus section) if it can be separately energized.   Within




an electrical section one may have a chamber-wise or field-wise




high tension split or both (see Figure 2-11).  The advantage of




splitting a mechanical section both chamber-wise and field-wise




is increased reliability with,  of course,  increased cost.  For




the applications under consideration, both inlet and outlet




sections are often split in the direction of gas flow.  In this




configuration the effects of variations in temperature and dust
                              2-57

-------
  MECHANICAL  SECTION  MECHANICAL SECTION   MECHANICAL SECTION
     FIELD-WISE
    CHAMBER-WISE
          t
[ELECTRICALLY  DIVIDED
 4  WAYS,  PARALLEL AND
       SERIES)
CHAMBER-WISE
      t
(ELECTRICALLY
DIVIDED 2 WAYS,
IN PARALLEL)
    FIELD-WISE
       t
(ELECTRICALLY DIVIDED
 2  WAYS,  IN SERIES)
               (DIRECTION OF GAS FLOW INDICATED BY ARROWS)

               Figure  2-11.  High tension splits.

 loading  across the chamber  because of poor  flow characteristics

 in  ductwork  leading to  these retrofit units are minimized.

 Reliability  is increased  at the inlet, which  is often  in  the

 half-wave mode.   If one  bus section  fails,  a  jumper cable  can  be

 engaged  to apply  full wave  to  the  "companion" bus  section  and

 thereby  prevent that  bus  section from failing.

      Reliability  relates  not only  to sectionalization  of  a given

 collection area but also  to the addition of collection area or

 electrical fields.  The  degree of  reliability can  be defined in

 terms of redundant capacity, which is a function of anticipated

 failure  and  time  between  maintenance periods.  Redundancy  may  be

 defined  as that additional  area in a precipitator  that compensates

 for the  "normal"  level  of unavailable collecting area.  To
                               2-58

-------
achieve a reliable yet cost-competitive design, one must have



detailed information on dust characteristics and a clear under-



standing of the effect of process variations on precipitator



performance.



     The basic consideration in energizing the precipitator is to




maximize the power input to achieve the highest collection



efficiency from a given collection area.  The decision on the




degree of sectionalization, however, is made quite independently



of the way in which the precipitator is to be energized.  The



number, size, and mode of operation (HW or FW)  of the T-R sets



can be manipulated to provide the required current density



within each bus section of the precipitator.  The size of the



transformer rectifer (TR) sets is selected to provide lower



current density at the inlet.



     In spark-limited operation, half-wave allows time during the



off-half cycle for recovery from the sparking condition (spark



quenching).   Complete decay of the charging field and of collec-



tion efficiency during the off-half cycle is avoided because of



the capacitive effect of high-resistivity dust, which tends to



maintain the field potential.



     In cases where the resistivity of the dust has been reduced,



i.e., because of in creased temperature of operation or high



carryover of carbon the capacitative effect of the dust is also



reduced.  Thus, the charging field decays move in half wave then



full wave.
                              2-59

-------
     The selection as to the mode of operation is site-specific,




and the variability of performance measurements in full-scale




precipitators may overwhelm any differences due to operation in




either mode.  In the processes under consideration,  half-wave




has been often used in the inlet fields and full-wave in the




outlet fields.




     In summary, precipitator sectionalization and energization




are based on maximizing the power input to the precipitator to




achieve the highest efficiency from a given collection area




while minimizing the potential for poor performance as a result




of various failure patterns.  The reliability of precipitator




performance is a function of process flow conditions and dust




characteristics, reliability requirements, and the designer's




experience.  The way in which a precipitator is energized depends




on the sectionalization configuration and the current density to




be supplied to each bus section, as determined by chemical and




physical characteristics of the dust, dust loading, and the gas




stream.  The number, size, and mode of operation of the T-R sets




can be fitted to the sectionalized configuration after bus sec-




tion design has been established.




2.3.2  Correlations^




     The foregoing discussion of precipitator design shows that




three parameters are of central interest:  gas volumetric through-




put (acfm); total collecting area  (ft ); and power density




(watts/ft  of collecting surface).  The graphical correlations




discussed  in this section relate these basic design variables  to
                              2-60

-------
process application.  The designer's judgment, experience, and




understanding of precipitator theory allow him to select the




values of overall mass collection efficiency, SCA, and power




density required for given process conditions and emission




standards.  A word of caution is needed, however.  It is not




intended that the approach presented here should be directly




applied to a specific site or installation.  In such applications




a number of very practical points must be considered, such as




design features to control and minimize large-scale turbulence,




gas sneakage, and particle reentrainment in the precipitator.




     The following discussion will examine some design trends




that have been established for precipitator sizing in the kraft




pulp mill industry.  The following processes are discussed:




     1)   Conventional recovery furnaces




     2)   Low-odor recovery furnaces




     3)   Bark/fossil-fuel boilers.




ESP Design Correlations - Conventional Recovery Furnaces--




     The basic pulping process is described in Section 2.1.1.  In




this section the effect of the various process parameters affect-



ing the performance of the electrostatic precipitators is examined




more closely.  For this purpose the important process parameters




are summarized in Table 2-9.
                               2-61

-------
         Table 2-9.  TYPICAL OPERATING CONDITIONS FOR

         PRECIPITATORS ON CONVENTIONAL RECOVERY FURNACES
    Particle size distribution
    Grain loading



    Particle material Sp. Gr.

     (75% Na2S04)



    Gas temperature



    Particle resistivity



    .Moisture content
x- = 1.4 •* 1.9 urn



c = 3.0 + 2.04



3-5  (gr/acf)



2 - 2.5





280 - 325 °F



10  - 10   ohm-cm



20 - 30% by volume
     Modified Deutsch >lodel--Matts and Ohnfeldt   proposed an



empirical modification of the classical Deutsch equation   that



essentially removes the size dependence from w, the particle

                                         _                   -^
migration velocity.  Their equation is:  n = 1 - exp (-w A/Q)
                                                        j\.


where k is said to be equal to 0.5 in most cases.  It can be



shown, however, that w  is dependent on the inlet particle size
                      JC

             14
distribution,   which changes with each application even if all



other characteristics of the precipitator are the same.


            14
     Feldman   proposed another efficiency equation of the form
               n- = 1-C
                       (w'A/Q)
                              m
                (Eq. 4)
Equation 4 has an advantage of separating all the effects of size



distribution into the constants C and m and of defining w1, which



is dependent only on the electrical energization of the precip-



itator and gas properties.  It should be noted that equation 4 is



still based on the Deutsch model and is subject to its assump-



tions and limitations.  The advantages over the Deutsch equation


                               2-62

-------
are that the "effective migration velocity" is replaced by a




quantity w1 which depends on the electrical and gas properties




and that the two constants C and m in equation 4 account for the




size distribution effects.  In the absence of abundant design




data, this equation was used to generate theoretical design lines




for precipitators on kraft recovery furnaces and bark/fossil fuel




fired boilers.  This equation has been confirmed in part by




available test data.  The derivation of equation 4 is discussed




briefly in the following paragraphs.




     The electrical force on a charged particle in an electric




field is given by:




               F = qE                                  (Eq. 5)





where E  (from the Deutsch model) is the electric field strength




at the precipitator collecting electrode.  (See Table 2-10.




Units are in the inks system.)   The force opposing particle




motion through the gas is:




               F = STTP dwd/CI                          (Eq. 6)




Equating forces and solving for the migration velocity of parti-




cles of size d:





               "d = 3^f                              (E^ 7)



CI is the Cunningham correction factor given by:




     CI = 1 + 2.5A/d + 0.84A/d exp (-.435/A)            (Eq. 8)




The particle charge q can be represented by the Cochet equation:
                              2-63

-------
              Table 2-10.  NOMENCLATURE FOR THE
          ELECTROSTATIC PRECIPITATOR COMPUTER MODEL
    A    = precipitator collecting area

    a    = particle-size-dependent parameter, Eq.  (11)

    C    = constant defined in Eq. (19)

   CI    = Cunningham's slip correction, Eq.  (8)

    d    = particle diamter

   E     = peak charging field

   E     = electric field near the collecting electrode
    P
    F    = Stoke's drag force on the particle

f, (d)    = inlet particle size distribution  function

  g(d)   = particle size dependent parameter, Eq.  (14)

   Kr    = particle relative dielectric constant

    k    = constant defined in Eq. (13)

    m    = constant defined in Eq. (19)

    n    = number of mechanical sections

    0    = volumetric gas flow rate

    q    = particle charge magnitude

    r    = particle fraction assumed reentrained at every
           mechanical section

  SCA    = specfic collection area

 SCAr    = specific collection area of precipitator on
           conventional recovery furnace

 SCAT    = specific collection area of precipitator on  low  odor
           recovery furnace

    w    = migration velocity

   w,    = migration velocity of a particle  of  size d

   w,     = overall effective migration velocity
    /C
[continued)                    2-64

-------
Table 2-10 (continued]
    w1     = modified migration velocity defined in Eq.  (22)

   w'      = modified migration velocity on conventional recovery
            furnace application

   w'      = modified migration velocity on low odor recovery
            furnace application

    x      = mass mean diameter

   E      = permittivity of free space

   '-.,      = collection efficiency of particle size d also
            efficiency correct for reentrainment loss r on
            particle size d

   "i*      = collection efficiency on particle size d without
            reentrainment

   ~      = overall collection efficiency of size d, EC.  (35)


    >'      = mean free path of gas molecules

   '»'      = empirical mean free path in Eq. (9)

    i.      = dynamic gas viscosity

    c      = geometric standard deviation of the particle  size
            distribution

    F.      = product
                              2-65

-------
where



     Kr = relative dielectric constant of the particle



and



     X1 = empirical mean free path



        = 0.1 ^m at  20°C and 1 a tin. pressure



     The Cochet equation accounts for particle charging by both



field charging and diffusion charging mechanisms.  This is



important in analyzing the effects of particle size, since the



charging mechanism changes from field charging to diffusion



charging in the submicron range.  Although there are more accur-



ate methods of computing particle charge than the Cochet equation,



these require numerical solution.  For the purposes of this



discussion, the Cochet equation is entirely adequate in repre-



senting the effect of particle size on charge.



     Combining equations 7 and 9 and defining




      * =  [(1 + ^cf)2 * II + 2X-/d)   (rV2^'       (E^ 10>



the particle migration velocity for particles of size d becomes:



           GEE

     w  =  ( G ° P)  aCId                                (Eq. 11)
      d      j u



     For particles of a single size, d,  the Deutsch equation can
be applied to calculate efficiency:
      1 - n )  = exp[-WdA] = exp [-(CoEoEpA) aCId]       (Eq. 12)
                      Q              3,Q

Defining new terms:




     k = £oEoEpA                                        (Eq. 13)

           3uQ



     g (d)  5 aCId                                        (Eq. 14)
                              2-66

-------
The single-size efficiency equation becomes:


      (1 - r,d) - exp[-kg(d)]                             (Eq.  15)


The overall collection efficiency  is  found by  integrating  over


the inlet size distribution, f   (d):


      (!-")=   o/°°  (I - nd) fI  (d)dd                  (Eq.  16)



Assuming a log-nornal inlet distribution this  becomes:
          -       1       TOO
        ~ M = vv^   ^  c/  exp[-kg(d)-0.5(r]dlnd(Eq.  17)
     If the integral in this equation could be evaluated directly,


one would have the overall efficiency equation in terms of x,  c,


and k; i.e. size-dependent variables would be distinguished from


the other variables.  However, the integral must be evaluated


numerically, and therefore no simple analytic expression for


efficiency is obtained directly.  It is possible to arrive


indirectly at a simple efficiency equation through use of equa-


tion 17.  The procedure is as follows.


     Equation 17 is solved numerically on the computer to obtain


different r. , k pairs for the typical inlet particle size distri-


bution in a recovery furnace, d ^ 1.7 urn, and x = 2.5.  The


results are plotted on log-log paper for  [-In (1-n) ] versus k.


As shown in Figure 2-12, this plotting yields a straight line,


which indicates a direct relationship between (1-n) and k.  The


equation of a straight line on this plot can be written as:
In
                     = m ln(k/k )                        (Eq. 18)

                               2-67

-------
    100
 c
 i
     1.0
     0.1
               J	L
_UL
       10"
                                          10'
Figure 2-12.
Plot of k versus -ln(l-n)  for  recovery
     furnace applications.
                          2-68

-------
                                 -               4
If C is defined as a value of  (1-n  ) when k  = 10  , equation  (1!
becomes:
     In
            InC



or
          Ind-nl
= m In (10 4k)                     (Eq. 19]
               M n~i- "i
      (!_-) = CUU  K)                                    (Eq. 20)


                                          -4
By referring to equation  (13), the term 10  k can be written as:




     10~4k = w1 |                                       (Eq. 21)



where


          L E E       _4
     w1 = —" ^ P  x 10                                  (Eq. 22)
            J H



Thus,  the desired efficiency equation is:



     1 - - = C(W'A/Q)m                                  (Eq. 23)



where w' is a modified migration velocity (its dimensions are



sec  ) and is independent of the inlet particle size distribution



but is completely dependent on the electrical energization of the



precipitator.



     Model application to conventional kraft pulp mills--To



generate absolute numbers for overall efficiency and SCA, w1 must



be estimated.  Available electrical data from field precipitators



(see Table 2-11) can be used to determine w', as follows:




     w. ; £°^EP x lO'4   (sec'1)




where E  is the peak charging field and E  is the average elec-



tric field near the collecting plate commonly known as the



collecting field.   Estimates of E  could be made knowing the



secondary voltage wave form to the precipitator and the absolute
                              2-69

-------
magnitude of the average secondary voltage at the discharge

electrode.  Generally full-wave rectifiers are used on kraft pulp

mill precipitators and the secondary average operating voltage is

on the order of 48 kv.  This results in
               48 x 103 x 2
           0    ' 6.1143                               (Eq. 24)

          EO = 5.95 x 105 (v/m)                        (Eq. 25)

   Table 2-11.  TYPICAL ELECTRICAL OPERATING DATA ON STANDARD
 9-INCH PLATE PRECIPITATOR WITH 0.109-INCH DISCHARGE ELECTRODES
Avg. secondary voltage at the
 discharge electrode

Avg. plate current density

Avg. power density
                                        45-55, kV avg

                                        10-50, mA/1000 ft
2
                                        1-2.5, W/ft
                                                   2
     Analytical expressions to estimate the collecting electric

field are relatively hard to derive in the case of wire-plate

precipitators.   A simple expression for E  can be derived for
                                          P
present purposes, assuming low current density.  '    Available

field data on a 9-in. plate precipitator with 0.109-in. diameter

discharge electrodes indicates that for this application, V  is

on the order of 23 kV average at 300°F.  For a typical operating

voltage of 48 kV average, it is estimated that E  will be on the

order of 4.5 x 10  (V/m).  The dynamic gas viscosity  (•_) at 300°F

is theoretically estimated at

          p - 2.5 x 10~5  (Nt-s/m2)                      (Eq. 26)

Thus, substituting the various quantities in equation 22 one

obtains:

     w. = L15i_x_l_OlJ:JJL.5._95-X J^jjc.1^ x 105 x 1Q-4
                     3 x 2.5 x ..0

                              2-70

-------
          w' = 3.155  (s  )                               (Eq. 28)



Therefore, for the recovery furnaces on kraft pulp mills, the



design equation becomes:




                .      -,   /-i — »  1/m

          A     X     ln d-n)
          Q ~ 3.155     InC




The inlet particle-size-dependent parameters C and m are deter-




mined by solving equation 17 numerically on the computer for the




typical inlet particle size distribution of d = 1.7 ym and c =




2.5.  The values of C and m are:




     C = 0. 957; m = 0.89




This design equation for precipitator size on the conventional




kraft pulp process mill is given by:





          A     1     IrWT n>  1/0.89
          A _        In(l-n)
              __

          Q ~ 3.155  ln(0. 957)



To convert from mks to English units the value for A/Q (sec/m)  in



equation 30 should be divided by 0.197, thereby obtaining ft /1000



acfm.



     Figure 2-13 shows the design line predicted using equation



30 and the test data points from the various jobs on conventional



recovery furnaces.  Correlation between the predicted model



efficiency and the performance test data is excellent.



Precipitator Design Correlations for Low-odor Recovery Furnaces —



     Efforts of the pulp and paper industry to eliminate odorous



gases escaping from pulp mills often involve switching to the so-



called low-odor recovery process.  In this process the odor



levels are lower, but the particulates emitted have different
                              2-71

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2-72

-------
physical properties.  R.L. Bump   has summarized some important



differences that must be accounted for in sizing a precipitator



for a low-odor recovery furnace.  The differences affecting



precipitator performance are summarized in Table 2-12.
       Table 2-12.  DIFFERENCES IN PARTICULATE PROPERTIES

        IN CONVENTIONAL AND LOW-ODOR RECOVERY PROCESSES
Parameter
Temperature, °F
Moisture content, %
Bulk density, Ib/ft^
Tenacity
Sulfur content
Conventional
280-325
20-30
20-25
Moderate
Low
Low-odor
340-450
7-20
5-10
High
High
     The dynamic gas viscosity plays an important role in deter-


                                                 19
mining particle drag force.  Typical compositions   of flue gas



entering the precipitator on a conventional recovery boiler '(wet



basis) and a low-odor recovery boiler are shown in Table 2-13.



Assuming typical gas temperatures of 300°F and 400°F in conven-



tional and low-odor applications and assuming 1 atmosphere



absolute pressure, one can calculate the dynamic gas viscosities



for the two applications.  Calculation indicates that



          p low-odor
            conventional
                         = 1.15
(Eq.  31}
                              2-73

-------
        Table 2-13.  TYPICAL ANALYSIS OF FLUE GAS FROM

          CONVENTIONAL AND LOW-ODOR RECOVERY BOILERS19
Component, %
N2
co2
CO
°2
Temperature, °F
Dynamic viscosity,
Nt-s/m2 x 10~5
Conventional
62.3
12.6
0.08
1.93
23.10
300
2.07
Low-odor
73.64
14.9
0.09
2.27
9.1
400
2.39
Other important parameters in precipitator sizing are particle


size distribution, particle resistivity, the electrical current-


voltage data, and particle reentrainment.   Available particle


size data on the low-odor process indicates mass mean diameters


of about 1.5 ym and a standard deviation of about 2.5.    These


values are very similar to those of particulate from the conven-


tional recovery furnace.  Particle resistivity in the two pro-

                                                9
cesses is the same order of magnitude, around 10  ohm-cm.  The


electrical data could be different with lower operating voltages


on high-temperature, low-odor processes.  The peak charging


fields would be expected to be lower.  This effect would be


compensated for, however, by an increase in ion mobility and


higher precipitator current.  Preliminary calculations indicate


that the available electrical data do not explain the differences


in precipitator performance caused by greater temperature


fluctuations.
                              2-74

-------
     The tenacity of the dust and the bulk dust density are very



important in quantifying rapping reentrainment losses.  Although



only qualitative statements can be made in the absence of quan-



titative measurements, field experience indicates that in the



low-odor process the dust adheres very tenaciously to the collect-



ing plates.  To dislodge this dust sufficient rapping forces must



be applied to produce rapid acceleration parallel to the gas flow



(shear action).  With heavy rapping, vibrations can be induced



perpendicularly to the gas flow direction in addition to the



necessary shear action at the plate surface, which result in a



scattering of the agglomerate.  This can lead to reentrainment of



relatively larger fractions of the collected particulate in a



low-odor process than in the conventional processes.



     Dynamic viscosity of the flue gas determines the drag force



on the particles.  The higher the temperature, the higher will be



the viscosity, resulting in increased drag force on the particles.



As shown in equation 29, SCA is inversely proportional to w1, the



modified migration velocity, according to the precipitator model



presented in connection with the conventional recovery furnace



process.  Assuming that all things are equal in the two processes



except the gas dynamic viscosity, one can write



     SCA    w'


     SCA~ = wf = X-15                                  (E^  32)
        C    -LJ


Equation 32 illustrates that a precipitator applied to low-odor



process (operating at 400°F)  requires an SCA about 15 percent



higher than one on a conventional process (operating at 300°F.)
                               2-75

-------
A precipitator design line based on these calculations is shown

in Figure 2-14 for precipitator sizing on low-odor recovery

furnaces.  Additional test data are required to determine the

validity of equation 32.

Precipitator Design Correlations for Bark. Boilers in the Paper
Industry--

     The objective here is to outline the design method used to

size precipitators applied to collection of bark ash emitted from

power boilers.  This evaluation does not include emissions from

boilers fired with sea-soaked bark materials.   It is well known

that the low resistivity of bark ash can pose serious collection

problems.  Reentrainment losses are high.  Nevertheless, ESP's

have been used successfully on non-salt laden bark boilers.  Any

theoretical model would overpredict precipitator performance

unless the calculated efficiencies are corrected for rapping

reentrainment losses as is done in the model presented here.

     Details of the bark boiler combustion process are described

in Section 2.1.1.  For theoretical development purposes the key

parameters are summarized in Table 2-14.
                              2-76

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                                 2-77

-------
 Table 2-14.  TYPICAL OPERATING CONDITIONS IN PRECIPITATORS
                 ON BARK/FOSSIL-FUEL BOILERS13
Particle size distribution:

      Limited data on particle size analysis indicate  the
      following ranges

          x = 5 - 15  (ym)

          o = 2.5 - 4

     Grain loading:   0.5 - 1.5 gr/acf
     Particle material sp. gr.:  0.5 - 1.0
     Gas terperature:  300 - 400 °F
     Particle resistivity:  10"^ - 10^ ohm-cm
     Moisture content:  10 - 20% by volume

Typical Electrical _0_p_er_a_tJ.jTg_ Data  (average values)

     Secondary voltage at discharge electrode:   40  - 45
      (kV avg.) electrode                       2
     Plate current density:  20 - 60 mA/1000 ft
     Power density:   1.5 - 3 W/ft2


     Theoretical models—The Deutsch model used  earlier in  connec-

tion with recovery furnaces can be used as a basic  equation  with

no reentrainment.  The Deutsch equation for a single size  par-

ticle is given by

          "ij = efficiency without reentrainment

             = 1 - exp (-w A/Q)                         (Eq.  33)

Letting r be the fraction of collected material  reentrained  in

the gas stream as a rapping reentrainment loss,  one can  write

          nd =  d-r)^                                  (E3-  34)

where

       n, = efficiency corrected for the reentrainment loss  r.

Therefore, for the entire precipitator length one  can  write

          1 - nT = n(l-nd) = n{l-(l-r)nd}               (Eq.  35)

                              2-78

-------
where

       r]  = overall collection efficiency of  size d

Equation 35 can be further simplified if the  following assumptions

are made:  1) overall migration velocity remains constant;  2)  the

fraction of the material reentrained remains  constant for differ-

ent particle sizes; and 3) that the fraction  of material reen-

trained remains constant for each mechanical  section.

     With these assumptions equation 35 can be written to obtain:

          1 - -  = -1 - d-r) (1 - exp(-wdA/0) ) -n

or

          1 - r  = -r + (l-r)exp(-wdA/Q)}n             (Eq.  36)

where

       n = number of mechanical sections in the precipitator.

     The overall mass collection efficiency of the precipitator

can then be determined by integrating equation 36 over the

entire particle size distribution.  Therefore, mathematically one

can write

          d-7)  =  i°  (1--,T) f1(d)dd                    (Eq.  37)
                  o

Assuming a lognormal inlet particle size distribution, equation

37 can be simplified.   The final integration, however, requires

a numerical technique to establish the relationship between  r on

^i.

      Model  application to bark boilers--The method used here is

similar to that described above for recovery  furnaces.



     Eo = ^TTll43 X 2  = 5.07  x 105 V/m               (Eq.  38)
                              2-79

-------
Using the computer program and Cooperman's correlation for the
current-voltage information, we estimate
     E  = 3.7 x 10  V/m
      P
      y = 2.5 x 10~5 Nt-s/m2
     £  = 8.854 x 10~  coul/V-m
      Q
     w1 = 2.216 s~l
Therefore, for bark ash boilers the theoretical design equation
assuring no reentrainment becomes
                          1/m
     A =  f_±_^> An(l-~ A                             (Ec. 39)
     Q    \2. 216^ ^  InC  J
The values of m and C can be determined as explained in the
previous section.  Assuming x = 5 urn and c = 2.5 the calculated
values are
     C = 0.7166; m = 0.63
     To convert from mks to English units, the value for A/Q in
sec/m in equation 39 is divided by 0.197,  thereby obtaining
ft2/1000 acfm.
     The plot of SCA versus overall efficiency for bark/fossil
fuel-fired boilers is shown in Figure 2-15.  The efficiency
values with no reentrainment  (r=o) over-predict precipitator
performance and must be corrected for reentrainment losses.  Use
of the reentrainment model presented in this section  (at r=40  and
50%)  shows a closer correlation to available test data on the
two installations shown in Figure 2-15.  Field data generally
show a 40 to 50 percent loss in efficiency due to reentrainment.
     The model needs further testing with additional performance
test data before it can be widely applied as a design tool for
                              2-80

-------
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2-81

-------
sizing precipitators applied to bark boilers.   In Figure 2-15,

use of the model assumes a typical inlet distribution of x = 5

and a = 2.5.  The reference line has a slope of 0.5.
2.3.3  CajDiJt a_l_ a n d _Ann u a_l_ C o sts__o f E_l_e ctrost atic P r e cipitators
       on Kraft Pulp _Mill ^Applications

     Capital and annual cost correlations for electrostatic pre-

cipitators on kraft pulp mills were developed using predicted

SCA's from Figures 2-13 through 2-15, corresponding to conven-

tional (high-odor) recovery furnaces, low-odor recovery furnaces,

and bark/fossil-fuel boilers, respectively.  In addition to

standard Research-Cottrell sizing and costing criteria, computer

programs were used to develop the cost correlations.  The costs

are presented in Figures A. 2-1 to A. 2-6, in Appendix A-2.

     Precipitator capital costs to the user, normalized at year-

end 1977, include the flange-to-flange precipi tator , structural

support,  erection and installation, engineering, contingencies,

and warranty and acceptance.  Heat jackets are not  included for

recovery furnaces or bark/fossil-fuel precipitators.

     Annual costs consist of maintenance, labor, power consump-

tion (assuming $0.03/kWh), administration, overhead, and capital

charges  (taken at 15% of total capital investment) .  Depreciation

(assuming a 15-year accounting equipment life), interest, insur-

ance, and taxes constitute capital charges.

     Since capital investments for the low-odor furnace at. 99.8

percent  (Figure A. 2-3) are approximately the same  as those for

the conventional furnace at 99.9 percent, it is clear  that the
                              2-82

-------
low-odor option is more expensive.  The difference in efficien-


cies alone accounts for a 20 percent larger precipitator size


(SCA) for low-odor applications.  Furthermore, the drag-bottom


configuration associated with low-odor applications is more


expensive than the wet-bottom used in conventional recovery


furnace precipitators.


     For the efficiency ranges considered, it appears that the


cost of a heat jacket may add up to 5 percent to the cost of the


precipitator system as defined above.  Use of a heat jacket


depends on precipitator capacity, shell surface area, and operat-


ing and ambient temperatures.


     Annual costs are higher in low-odor  (Figure A.2-4)  than in


conventional (Figure A.2-2)  applications.   Since capital invest-


ments are higher for low-odor precipitators,  the capital charges


are correspondingly higher.   Furthermore,  low-odor precipitators


have higher power density (1.9 W/ft  versus 1.5 W/ft  for con-


ventional precipitators)  and hence direct operating costs are


higher.


2.4  MECHANICAL COLLECTORS


2.4.1  General System Characteristics


     This section describes the major parameters that must be


considered in the design of a mechanical collector servicing


bark/fossil-fuel boilers.  The most common type of mechanical


collector is the conventional cyclone.


2.4.2  Design Philosophy

                                                 21
     Parameters affecting the design of a cyclone   are presented


in Table 2-15,  and described in the text that follows:

                              2-83

-------
        TABLE 2-15.   PARAMETERS  AFFECTING  CYCLONE  DESIGN21
     System input
   System
 parameters
          System
          output
Process application
Process conditions
Applicable emission
 standard
Pressure drop
Particle size
 distribution

Inlet gas
 velocity

Cyclone body
 diameter dimen-
 sion ratios

Specific gravity
 of dust
Overall collection
 efficiency

Capital investment
Annual cost
Pressure Drop--

     Pressure drop is one of the most important factors affecting

efficiency and design.  The pressure drop across a cyclone varies

as the square of the gas volume and is directly proportional to

the density of the dust-laden gas.  The total pressure drop in a

cyclone is the sum of separate losses in the inlet flue, the

cyclone body, and the outlet duct.

Particle Size--

     The efficiency of a conventional cyclone decreases with

decreasing particle size to a point where particle collection is

50 percent at a particle diameter of 5 um.  The finer particles

are strongly influenced by turbulence of gas flow and are not

collected.  The effect of particle size on efficiency of a specif-

ic type of cyclone is shown in a fractional efficiency curve,

which can be obtained only from test data    (See Figure 2-16).
                              2-84

-------
                              AIR AT 70°F
                              RESISTANCE 3.0 in.  WATER GAUGE
                              LOAD 46 g/ft3
                              sp. gr. 2.1
                                             I
                        10    15    20    25    30
                          PARTICLE DIAMETER,  ym
35
40
                                                          22
       Figure  2-16.   Typical  fractional  efficiency curve.

Cyclone Body and Diameter  Dimension  Ratios—

     A cyclone of relatively  higher  efficiency and higher  pres-

sure drop could be designed by  1)  increasing  the length of the

cyclone, 2) decreasing  the width  of  the  inlet,  or 3)  increasing

the ratio of body diameter to outlet diameter,  while  at the same

time reducing  the body  diameter.   Increasing  the length of the

cyclone body provides a  longer  residence time for gas in the

cyclone and therefore more revolutions of the gas stream.   In-

creasing body  length also minimizes  efficiency loss due to reen-

trainment of particles  in the ascending  vortex.   Increasing the

ratio of body diameter  to the gas  outlet diameter effects  an in-

crease in efficiency at  ratios  up  to about  3  to 4;  above a ratio

of 4, the gains are slight but  the pressure drop increases.

Specific Gravity of the  Dust--

     Of the dust physical properties affecting  the  collection
                              2-85

-------
efficiency of a cyclone, specific gravity is one of the most



significant.  Efficiency is greater with particles of higher



density than with those of lower density.  It is the specific



gravity of the particle, and not the bulk density of the dust



that is important.   However, bulk density of the dust is an



important design consideration.


                         23
     Tables 2-16 and 2-17   summarize the effects of cyclone



design parameters.



2.5  WET SCRUBBERS



2.5.1  Gen era 1 __Sy_s_t_e_m_ Characteristics



     The sources of particulate  emissions to which wet scrubbers



are applied are smelt dissolving tanks,  sludge lime kilns, and



more recently combination bark/fossil-fuel boilers at kraft pulp



mills, and conveyors and crushers in stone crushing operations.



Types of wet scrubbers used are  impingement, packed towers,



showered mesh mist eliminators,  and Venturis.



     Exhaust gases from a lime kiln normally pass through a mech-



anical cyclone collector for lime dust recovery and finally



through a liquid scrubber for particulate control.  The major



types of scrubbers used on lime  kilns are impingement and venturi



scrubbers.  Impingement scrubbers have been used extensively for



particulate scrubbing on lime kilns because their low pressure



drops and low scrubber shower rates minimize operating costs.  A



disadvantage of the impingement  scrubber is a limit on the solids



concentration in the scrubber slurry because of plugging potential.



They are also less efficient than other  scrubbers in removing



particulate matter because the gas-liquid contact is less efficient.


                              2-86

-------
Table 2-16.   PERFORMANCE TRENDS BASED ON  CHANGES IN
                 CYCLONE DESIGN
Change
Increase cyclone size
Lengthen cylinder
Increase ir. " et area,
maintain volume
Increase inlet area,
maintain velocity
Lengthen cone
Increase size of cone
opening
Decrease size of cone
opening
Lengthen clean-gas out-
let pipe internally
Increase clean-gas out-
let pipe diameter
Performance trend
Pressure loss
Down
Slightly lower
Down

Up
Slightly lower

Slightly lower

Slightly higher
Up
Down
Efficiency
Down
Up
Down

Down
Up

Up or down

Up or down
Up and/or
down
Down
Cost
trend
Up
Up
No effect

Down
Up

No effect

No effect
Up
Up
                        2-87

-------
Table 2-17.  EFFECTS  OF  PHYSICAL PROPERTIES AND PROCESS
              VARIABLES  ON EFFICIENCY
Proportional
change
Gas change
Increase velocity

Increase density

Increase viscosity
Increase temperature
(maintain velocity)
Dust Change
Increase soecific
gravity
Increase particle
size
Increase loadings
Pressure
loss

Up

Up

Negligible

Down


No effect

No effect
No effect
Efficiency

Up

Negl igible
change
Down

Down


Up

Up
Up
Cost
trend

Initial cost down
Operating cost up
Slightly higher

No effect

No effect


No effect

No effect
No effect
                         2-88

-------
Capital costs of impingement scrubbers are higher than costs of



venturi scrubbers on similar installations because the impinge-



ment scrubbers are larger and more complex.  Newer kraft pulp



mills are installing venturi scrubbers on the lime kilns because



of their higher particulate removal efficiencies.  Venturi scrubbers



can operate with slurry water solids concentrations of up to 30



percent by weight without excessive plugging.  Some operating



characteristics of particulate scrubbers on kraft lime kilns are


                        24
presented in Table 2-18.



    Table 2-18.  OPERATING CHARACTERISTICS OF PARTICULATE

              LIQUID SCRUBBERS ON KRAFT LIME KILNS
Parameter
Liquid/gas ratio,
(gal/1000 ft3)
Slurry solids, %
Pressure drop, mm
(in. H20)
Power required,
(hp/ton/day )
Power required,
(hp/ton/day)
liter/in
by wt
Hg
kW per ton/day
kW per ton/day
Scrubber type
Impingement
0.54-2.0
(4-15)
1-2
9-13
(5-7)
0.041-0.049
(0.05-0.06)
(0.13-0.16
(0.16-0.20)
Venturi
1.73-3.21
(13-24)
10-30
19-28
(10-15)
0.082-0.099
(0.10-0.12)
0.27-0.34
(0. 33-0.42)
  per mass of pulp


  per mass of lime



     The particulate matter from kraft smelt dissolving tanks



consists of both dissolved and undissolved NaOH, Na_CO_., and
Na
_S.   Typical particulate emissions from smelt dissolving tanks
are 0.03 to 1.2 kg per Mg of pulp  (0.05 to 2.3 Ib/ton) following
control devices.
                25
                  Most of the smelt tanks that are controlled
                              2-89

-------
use mesh demisters and/or packed towers to collect particulate

matter from exhaust gases.

     Typical operating conditions for two recently installed ven-

turi scrubbers on combination bark/fossil-fuel  boilers are

summarized below:

                         Pressure drop,
     Volume acfm           in.  W.G.           L/G (gal/1000 ft3

     74,575 at 390°F        8-10                6.7 - 8.0
    174,000 at 395°F       15-20                   8.5

     The following are operating conditions specified for venturi

scrubber operations on crushers:

                    Pressure drop,  in.  W.G.    L/G gal/1000 ft3

At 20,000 acfm              7-17                     9-13
At 70,000 acfm              9-16                     9-13

The ranges of pressure drops and L/G ratios are attributed to

different levels of scrubber efficiency.

     The following are operating conditions specified for venturi

scrubbers at conveyor transfer points:

                         Pressure drop,
                           in.  W.G.           L/G gal/1000 ft3

     At 5,000 acfm           7-12                   8-9
     At 15,000 acfm          7-12                   8-9

Impingement Scrubbers--

     In an impingement scrubber the  gas stream enters the collector,

then passes over a pool of water and impacts the surface of the

pool before exiting.  Control of the water level is critical to

this device.  Pressure loss and efficiency are determined by the

liquid level.  This type of collector functions well in the pres-

sure drop range of 2 to 6 in.  Inlet loadings range from 3 to

                              2-90

-------
14 gr/acf, and outlet emissions range from 0.4 to 1.5 gr/acf.




Although it is advantageous to attempt sludge separation inside




the scrubber, the dust tends to stay in suspension in the sump




because of air turbulence.  Nevertheless, where particles are




large and settle easily, this can be a very successful arrange-




ment.  Because the liquid in the pool serves as the scrubbing




medium, the liquid discharge rate can be adjusted according to




the desired solids content in both the retained liquid pool and




the discharge sidestream.




Packed Towers--




     Packed vertical towers contain materials on which the gas




and liquids are contacted.  Raschig rings are the most common




packing materials.  The gas stream can be introduced across, with,




or against the flow of liquid.  In the crossflow design, liquid




is introduced at the top of the packing, while the gas moves




horizontally through it.  This arrangement helps to wash any accu-




mulated contaminants off the packing surface.  In the cocurrent




flow design, gas and liquid enter at the top of the scrubber




and leave at the bottom.  The exit gas stream then passes through




an entrainment separator or mist eliminator.   In the countercur-




rent design, the liquid flows down through the bed, wetting the




packing to provide interfacial surface area for mass transfer of




the pollutant with the gas.  The gas then flows up the bed counter-




current to the liquid.  Highest pressure drop and lowest gas flow




are achieved with the countercurrent unit; gas flow capacity is




greatest in the cocurrent unit, and operation of the crossflow
                              2-91

-------
tower is unpredictable.  All three designs are subject to partic-



ulate buildup on the walls.   Clean liquid and low dust loading



are desirable.  Water is introduced above the packing by weirs or



spray nozzles.  Packed towers must be operated within a narrow



range of conditions to prevent maintenance problems.   If either



the liquid or gas rate is accelerated, liquid holdup  occurs and



pressure drop increases.  If gas velocity is further  accelerated,



flooding occurs, accompanied by high pressure drop and entrain-



r.ent of liquid in the gas stream.   Buildup of solids  in the pack-



ing is a serious problem.  Unlike  other scrubbers, packed tower


                                    2 8
internals are not easily accessible.



Showered Mesh Mist Eliminators--



     Particulate matter consisting of dissolved and undissolved



NaOH, Na CO , and Na2S is emitted  from the smelt tank with the



flow of gases.  The mist eliminator consists of fine  wire mesh



screens approximately 30 cm  (1 ft) thick.  Droplets condense from



the gas on the wire mesh screens,  which may be placed in series



as determined by the absorption efficiency required.



     Collection efficiency can be  increased by following the mesh



mist eliminator with a packed tower or by using a packed tower



only.  Table 2-19 summarizes the efficiency of mesh demisters



used in conjunction with another wet scrubber on smelt dissol-


           29
ving tanks.
                              2-92

-------
      Table 2-19.  PERFORMANCE CHARACTERISTICS OF SHOWERED
          MIST ELIMINATORS ON SMELT DISSOLVING TANKS29
Control device
Pad entrainment
Separator
Separator
Separator
Separator
Separator
Pad plus shower scrubber
Pad plus packed scrubber
Packed scrubber
Collection
efficiency, %
71.8
77.2
77.8
90.2
93.4
70.8
96.2
91.9
98.1
Emission rate,
Ib/ton
(0.05)
(0.15)
(0.63)
(2.3)
(1.2)
(1.58)
(0.41)
(1.20)
(0.05)
Venturi Scrubbers—

     In conventional terminology, the venturi scrubber is cate-

gorized as a gas atomized spray scrubber.  The collection process

mainly relies upon acceleration of the gas stream to provide im-

paction and intimate contact between the particulates and fine

liquid droplets generated as a result of gas atomization.  Basi-

cally, this is a high energy consuming device designed for high

particulate collection e-fficiency.  Typically, the pressure drop

is on the order of 10 to 20 in. of water or more in kraft pulp

mill applications.  Collection efficiency increases with the pres-

sure drop and liquid-to-gas circulation ratio.  However, there is

an optimum L/G ratio above which additional liquid is not effec-

tive at a given pressure drop.  In this device the pressure drop

can be increased by increasing the gas velocity.

     The system characteristics and design philosophy for wet
                               2-93

-------
scrubbers applied to stone crushing and conveyor transfer points




are similar in many respects to the information presented for




kraft pulp mill applications.  One difference is that hoods and




sometimes extensive ductwork are required to collect and transfer




emissions from primary, secondary, and tertiary crushers to the




scrubber inlet.  The system consists of a venturi scrubber, re-




circulating tank, pumps, slurry settler, slurry filter, and




induced-draft fan.  A system for conveyor transfer points requires




less ductwork than one for crushing operations.




2.5.2  Design Philosophy




     Where local emission regulations are strict regarding kraft




pulp mill and stone crushing operations, venturi scrubbers are




often used when scrubbers are specified.




     In design of a venturi scrubber, the key parameters affect-




ing particulate collection are gas velocities and gas flow rates,




particle size distribution, pressure drop, and liquid-to-gas ratio




In addition, the following information is also required for




selection of equipment.




     (a)  Gas handling capacity per module.




     (b)  Total number of modules required.




     (c)  Capital investment; annual costs.




     (d)  Water requirement; water recirculation.




     (e)  Availability of the equipment or necessary downtime.




     (f)  Fractional collection efficiency of the device.




     (g)  Total power consumption as a fraction of the generated




          power.







                               2-94

-------
Velocity/Gas Flow Rate—




     Sizing of a venturi scrubber is often based on the inlet gas




velocity and flow rate.  Usually, the inlet gas velocity is about




60 ft/sec while the inlet gas rate is dependent on the designed




scrubber diameter.  Typical scrubber diameters are under 10 ft.




If the gas rate is too high to be accommodated by one scrubber,




several scrubbers should be designed for the system.




     The gas velocity through the venturi will decrease more at




higher temperatures than at lower temperatures.  Also, at higher




temperatures higher liquid-to-gas ratios are required for heat




transfer.




L/G Ratio—




     The L/G ratio typically ranges from 1 to 15 gpm/1000 acf for




all of the scrubbers discussed and is basically a function of




inlet gas temperature, inlet solids content, and method of water




introduction.    At higher inlet gas temperatures, evaporation of




the scrubbing liquor may occur at the point of gas/liquid con-




tact.  Where inlet dust loading is heavy, the L/G ratio should be




increased to minimize solids buildup and plugging of drains.



Although pressure drop across the venturi is essentially inde-




pendent of specific design, the less efficient methods of water




introduction will require additional scrubbing liquor to meet




efficiency requirements.




Pressure Drop—




     Design for a given application requires consideration of




throat velocity and L/G ratio to achieve the maximum collection
                              2-95

-------
efficiency for the energy spent.   The energy spent is often




indicated by the gas pressure drop across the scrubber,  which




ranges typically from 10 to 20 in. H_0 for venturi scrubbers, 2




to 6 in. for impingement scrubbers, 1 to 2 in.  for packed towers,




and 0.05 to 1 in. across a 4-in.  bed in a mesh mist eliminator.'




Achieving a given pressure drop depends on the relationships




between throat velocity and L/G ratio.  Actually,  only one set of




conditions will yield the maximum efficiency for the energy




spent.  That one set of conditions is the only one that will




create maximum droplet surface with a minimum L/G  ratio during




atomization.




Particle Size Distribution--




     The particle size distribution in the inlet gas stream, a




key factor in control equipment design, often varies with process




operating conditions.  Data on fractional collection efficiency




for submicron particles are particularly difficult to obtain.




When one is speaking of greater collection efficiencies, it.



should be clear that this means increased fractional collection




efficiencies in the submicron particle size range.




Materials Selection--




     Because scrubber slurry and the gas streams often carry




abrasive solids that can erode, selection of construction




materials must be considered.  Where abrasion-resistance require-




ments exceed the limits of stainless steel, the designer may




select fiberglass reinforced plastic  (polyester).   Abrasion-




resistent liners are also needed to withstand high temperatures.
                              2-96

-------
Mist Eliminator--



     Mist eliminators are necessary to control undesirable emis-




sions of liquid droplets from the scrubber, caused by atomization,




and carryover of some liquid during scrubbing.




     Because of the solids in the scrubber liquor, entrainment of




water droplets can cause system operating problems as well as




liquid losses.  Suspended or dissolved particles can cause solids




buildup, and suspended solids can cause erosion.  Among the many




problems caused by buildup of solids is the resultant increase in




pressure drop.




2.5.3  Correlations




     Another difficulty in designing venturi scrubbers, impinge-




ment scrubbers, packed towers, and shower mesh demisters is the




unavailability of reliable design models.  Nearly all of the




published scrubber models show either by formulas or by design




curves that the empirical correlations are based on inertial im-




paction or overall power input.   Usefulness of empirical models




is often limited because both control and process variables vary




within certain ranges.  Therefore, extrapolating design data from




empirical models involves some risk.  Moreover, particulate col-




lection in all four types of scrubbers depends not only on




particle size distribution but also on particulate properties,




such as specific gravity, wetability, agglomeration, and solu-




bility in the scrubber liquid.
                             2-97

-------
                                   32
     The K-factor in Brink's model,    f-factor in Calvert's


      33                                                 ~;4
model,   and the 8 and y constants in the Power-Law model"  are



all empirical constants encompassing many of the parameters upon



which particulate collection depends.  Which model is suitable is



a matter of judgment.  In addition,  other mechanisms such as



diffusion may control collection of submicron particles.



     The model used in this report was developed by Research-



Cottrell and is presented in detail in Section 4.2.2.  It has



been used for the general class of gas atomized spray scrubbers.



It is specifically intended to model flooded-disc scrubbers.  Al-



though the model was developed specifically for fly ash applica-



tions, we extrapolate for use here in the absence of fractional



efficiency data on kraft pulp mill and stone crushing applica-



tions.  The similarity of some of the dust properties and required



pressure drops indicates that extrapolation appears reasonable.



     The L/G ratio, pressure drop, and efficiencies calculated



from this model are used as a basis for capital and annual cost



evaluation, presented in Section 2.5.4.  An optimum L/G ratio



was chosen, and the pressure drop increased to achieve the



desired collection efficiency.



2.5.4  Cajgital and Annual Costs of Venturi Scrubbers on Kraft

       Pulp Mill _and_5_tone _Crushing Operations



     Capital and annual costs are presented in Appendix A-5.



These are based on application of a flooded-disc scrubber to



collect particulate emissions.  The computer model is based on



the following assumptions.
                              2-98

-------
The major equipment included in the venturi scrubber




system consists of a flooded disc scrubber and a mist




eliminator with a sump tank, one forced-draft fan with




driver, and two slurry pumps with drivers.  The aux-




iliaries included are ductwork, expansion joints,




piping, and instrumentation.




The material of construction for both major equipment




and auxiliaries is carbon steel without linings.




The temperature of the flue gas is 400° to 500°F in lime




kilns and 200°F in smelt dissolving tanks.  Control




systems applied to stone crushing operations operate at




ambient temperature.




The total capital investment for the system consists of




the major and auxiliary equipment costs, tax and freight




(average),  installation costs,  engineering,  and con-




tingency.




The annual costs consist of:




     (1)  Fixed charges (at 15 percent of the total




     capital investment)  including depreciation, interest,




     insurance, and taxes.



     (2)  Maintenance (at 5 percent of capital invest-




     ment)  including materials  and labor.




     (3)  Labor cost (at $9 per  man-hour assuming 3500




     man-hours per year required).




     (4)  Administration (at 10  percent of labor cost).




     (5)  Water usage (at $0.30  per 1000 gal).




     (6)  Electricity usage (at  $0.03/kWh)



                   2-99

-------
               (7)  Overhead cost (at 10  percent  of  the  total  cost




               of water,  electricity,  labor,  and maintenance).




     6.   Cost estimates  are based  on  costs  of materials  and




          labor in the 4th quarter  of  1977.




     7.   Dust specific gravity is  taken to  be 2.4  g/cm  for




          kraft pulp mills and 2.7  g/cm   for stone  crushing




          operations.




     Figure 2-17 shows the system components and boundaries.




     Figures A.3-1 and A.3-2 indicate  the capital and annual




costs, respectively, for  venturi scrubbers on sludge  lime kilns.




For a system with high gas temperature and high  required  effi-




ciency of particulate removal, a gas precooler may  be required  to




reduce the effects of high temperatures  on scrubber performance




as well as on cost of fans.  The power consumption  of the fan has




a considerable effect on  the total  operating cost in  high-pressure-




drop operations.




     Figures A.3-3 through A.3-6 present capital and  annual  costs




of venturi scrubbers applied to non-salt and salt laden bark/




fossil fuel fired boilers respectively.   The presence of  salt




in the fuel can severely limit the  efficiency of the  venturi




scrubber at the maximum estimated pressure drop  of 20 inches  of




water.  This reduced efficiency has been confirmed by field tests




of a venturi scrubber at  similar pressure drops  and L/G ratio




as the data presented here.




     The result of having salt in the fuel is that capital and




annual cost for the salt  laden venturi scrubbers are higher
                              2-100

-------
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2-101

-------
than the non-salt scrubbers, but far less removal of particulate,




is provided.




     Since the particles emitted from crushers are coarser than




those from conveyors, a lower pressure drop will effect a higher




collection efficiency (compare Figure A.3-7 with Figure A.3-9).




Figures A.3-8 and A.3-10 show clearly the strong effect of elec-




tric power consumption on total operating costs of both crushers




and conveyors.  In high-efficiency operations, nearly all of the




power consumption is attributed to the fan.  The fixed charges,




such as equipment depreciation, interest, taxes, and insurance,




are considerably smaller than the cost of fan operation.  Labor,




maintenance, water usage, and overhead are grouped into the




"others" category.




2.6  FABRIC FILTERS




2.6.1  System Characteristics




     Within the kraft pulping operation, the application of




fabric filtration for control of particulate emissions is limited




to bark or bark/fossil fuel-fired power boilers.  The design




parameters discussed in this section are derived from three known




baghouse installations at two mills, Simpson Timber Company in




Shelton, Washington, and Long Lake Lumber Company in Spokane,




Washington.   A fourth baghouse system has recently been purchased




by a Georgia-Pacific mill in Bellingham, Washington, but is not




yet installed.  Table 2-20 lists the pertinent design criteria




for power boiler applications based on two of the currently




operational systems and the proposed new unit.






                              2-102

-------
         Table  2-20.   DESIGN PARAMETERS FOR KRAFT PULP
                    POWER BOILER BAGHOUSES

Volume flow rate, acfm
Inlet gas temoerature,
Op
A/C ratio, ftVacfm
Bag cleaning method
Pressure drop, in. H_0
Bag fabric
Precollector
Material handling
system
Simpson
Timber
230, 000
500
A . 5
Pulse jet
9-9. 5
Teflon
coated
fiberglass
Mechanical
cinder
collector
Screw con-
veyor
Long Lake
Lumber
25,000
400
4.0
Pulse jet
5.8-6.8
Nomex
None
Screw con-
veyor
Georgia-Pacific
180, 000
440
4.0
Pulse jet
a
Teflon coated
fiberglass
None
Screw conveyor
Collector not yet installed.
                             2-103

-------
     Fabric filtration is the preferred method of  particulate




control in the crushed stone industry because of the dry,  inert




mature of the emitted dust collected at ambient conditions.




Also, since the captured dust is often used as a stone product or




is recycled within the plant, baghouses are ideally suited to




this industry.  The collectors used to control the various unit.




operations employ the same basic design parameters and usually




differ only in size depending on the number of ventilation points




in the system.  Typical design parameters for baghouses serving




drilling, crushing, screening transfer operations  are shown in




Table 2-21.s




     Data gathered by the EPA during emission tests on the 12




baghouse units (listed in Table 2-21) used to control a variety




of rock types, including limestone, traprock and cement rock, in-




dicated that the size distribution of particulates collected, the




rock type processed, and the facility controlled do not sub-




stantially affect baghouse performance.



     Parameters important to fabric filter system design include




air-to-cloth ratio, pressure drop, cleaning mode and frequency of




cleaning, composition and weave of fabric, degree of sectionali-




zation, type of housing, and gas cooling.  Baghouses are rela-




tively insensitive to process variables such as chemical compo-




sition (providing that the correct bag fabric is chosen) ,  part-




icle size, electrical resistivity, etc.; thus, there tends to be




very little substantial design difference from one application,




or indeed from one manufacturer, to the other, when comparing






                             2-104

-------
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                                   2-105

-------
baghouses with the same cleaning mechanism.   Differences that do



exist are generally related to maintenance (e.g.,  number of bag



rows accessible from a given interior walkway;  method  of bag cuff



attachment to cell plate;  etc.).  Pertinent  baghouse  design



criteria are briefly discussed below.



Air-to-Cloth Ratio—



     A major factor in the design and operation of a  fabric



filter, the air-to-cloth (A/C) ratio, is the ratio of  the quanti-



ty of gas entering the filter (ft /min)  to the  surface area of


              2                                          3
the fabric (ft ).   The ratio is therefore expressed as ft"/min



per ft ,  or sometimes also as filtering  velocity (ft/min).   Most



often only the first member of the ratio term is given, e.g., an


                               3               2
A/C ratio of 1.5 implies 1.5 ft /min per 1.0 ft .   In  general,



lower ratios are used for filtering of gases containing small



particles or particles that may otherwise be difficult to cap-



ture.  Selection of the ratio is based on industry practice or



the recommendation of the filter manufacturer.



     Design A/C ratios for power boiler  fabric  filters are about



4/ or 5/1.  The three units in operation have A/C ratios of 4/1,



4.8/1, and 4.5/1.   The new Georgia-Pacific baghouse will have a



4/1 net A/C ratio.  Most of the particulate emitted from bark



boilers tends to be in the submicron to 10 urn size range.  Thus,



enough of the larger particles are present to allow use of a



fairly high A/C ratio, but the amount of fines in the mix pre-



vents the A/C ratio from being raised much further.  Higher



ratios may result in excessive pressure drops.   An example of
                              2-106

-------
this problem is seen at one of the installations at Simpson



Timber.  The pressure drop is 3 in. above design and the par-



ticulate size distribution is skewed largely toward the submicron



range  (much of the particulate consists of NaCl from the sea-



soaked bark).



     Design A/C ratios for fabric filters on crushed stone opera-



tions range from 5.0/1 to 7.0/1 for pulse jet units and 2.0/1 to



3.1/1 for shaker units.



Pressure Drop--



     Pressure drop in a fabric filter is caused by the combined



resistances of the fabric and the accumulated dust layer.  The



resistance of the fabric alone is affected by the type of cloth



and the weave; it varies directly with air flow.  The permeability



of various fabrics to clean air is usually specified by the manu-


                                 3                  2
facturer as the air flow rate (ft /min)  through 1 ft  of fabric



when the pressure differential is 0.5 in. H_0 in accordance with



the American Society of Testing and Materials (ASTM).  At normal



filtering velocities, the resistance of the clean fabric is



usually less than 10 percent of the total resistance.    The



spaces between the fibers are usually larger than the particles



that are collected.  Thus the efficiency and low-pressure drop of



a new filter are initially low.   After a coating of particles is



formed on the surface, the collection efficiency improves and the



pressure drop also increases.  Even after the first cleaning and



subsequent cleaning cycles, collection efficiency remains high



because the accumulated dust is not entirely removed.
                              2-107

-------
     The pressure drop through the accumulated dust layer has




been found to be directly proportional to the thickness of the




layer.  Resistance also increases with decreasing particle size.




Even though several studies have been devoted to filtration




theory, it is difficult to relate collection efficiency and




pressure drop  on an industrial scale.




     The range of operating pressure drop for bark boiler bag-




houses is 6 to 12 in.  H.,0, and it is preferable to operate at




the lower end of this range.




     Pressure drops across fabric filters in crushed stone opera-




tions from respondents in this study, fall in the range of 2 to 8




in. HO.  Pressure drops are normally higher in collectors used




on tertiary crushing and screening operations than in those used




on primary crushing because of the smaller particle sizes en-




countered.




Cleaning of Fabric Filters--




     Table 2-22 shows various cleaning methods that are used to




remove collected dust from fabric filters to maintain a nominal




pressure drop of 2 to 6 in. H_0.  A discussion of the operation




of various cleaning methods is presented in Section 3.3.




     Each method has advantages and disadvantages.  For example,




when reverse air is used with a ringless bag, it creases the bag




considerably and narrows the cross sectional area available for




reverse flow to occur.  This can be alleviated by use of anti-




collapse rings.  The mechanical shaker is usually applied in a




horizontal fashion to minimize flex abrasion  (fiberglass bags),
                              2-108

-------
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                       2-109

-------
which shortens the life of glass fabric.   The pulse jet method,




which uses jets and short bursts of compressed air, dislodges the




dust from the bag wall during filtering to eliminate off-line




cleaning.




     The reverse air method is the most gentle of the three




methods discussed above, and it promotes longer bag life.   How-




ever, this method alone may not provide adequate cleaning  and may




be used in combination with shake or pulse jet (with less  pres-




sure) methods to increase the effectiveness of cleaning and




minimize bag wear.




     All three baghouse installations on bark boilers use  pulse




jet as the cleaning mechanism.  Simpson Timber Company initially




used reverse air and pulse jet for cleaning at its Shelton,




Washington, baghouse, but discontinued the reverse air after




finding it to be ineffective.  Installations in the crushed stone




industry use pulse jet and shaker mechanisms in about equal




numbers.




Frequency of Cleaning--




     The cleaning cycle should be as short as possible so  that no




sizable portion of the total fabric will be out of service at any




given time.  With shake cleaning equipment, for example, a common




ratio of cleaning to deposition time is 0.1 or less.    With a




ratio of 0.1, 10 percent of the compartments in the baghouse are




out of service at all times during operation.  Therefore,  the




frequency of cleaning should be designed to minimize this  ratio.




As mentioned previously, with pulsing equipment, the cleaning





                             2-110

-------
time is very brief, yielding a very low ratio of cleaning time to
filtering time.
Selection of Fabric--
     Selection of fabric is generally based on the operating tem-
perature and on resistance of the fabric to abrasion and corro-
sion.  Table 2-23 shows typical characteristics of various fabrics,
which include cotton, wool, fiberglass, and other man-made
fibers.    Many fabric weaves are available; or the fabric may be
felted, a process whereby the identity of the separate yarns
tends to be replaced by a more uniform mat.  Felted fabrics are
almost always cleaned by reverse jet or pulse jet methods.
Fabric characteristics may also be altered by further treatment
for specific purposes, such as to decrease adhesion or improve
wearability.  Silicones are often used on fiberglass to reduce
abrasion.
     Since inlet gas temperatures on kraft pulp mill power
boilers range as high as 500°F, the bag fabric must be heat-
resistant.  The two Simpson Timber units contain Teflon B-coated
fiberglass bags for operation at 500°F.  The Long Lake baghouse
uses Nomex bags and operates at a temperature of about 410°F.
The new unit at Georgia-Pacific will use Teflon coated fiberglass
for operation at 440°F.  The preferred cleaning mechanism for the
collector is pulse jet (flex cleaning), which allows for maximum
filtering time and minimum interruption of the filtering flow.
It also allows for a slightly smaller-sized collector.
     At temperatures below 275°F, as is the case in the crushed
stone industry, polyester is preferred.
                             2-111

-------









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2-112

-------
Degree of Sectionalization--


     Design of fabric filter sectionalization (the number of


separate filter compartments)  requires knowledge of the variation


in gas flow with respect to process or plant ventilation, the


sizes of commercially available units, and the expected frequency


of maintenance.    Individual  compartments in small collectors

                               2
may contain as little as 100 ft  of fabric surface, although some


large units with a capacity of 50,000 ft /min may have only one


compartment.    Except in reverse jet and pulse jet units, at


least one compartment in any collector is out of service during


the cleaning cycle.


Filter Housing--


     Configuration of the filter housing depends on the required


fabric surface area and on the temperature,  moisture content, and


corrosiveness of the gases.  When the baghouse is designed so


that the dirty gas enters the  inside of the  bags under positive


pressure, housing may be needed only for weather protection or


for emission measurements.


     The floor area required for baghouses depends on the filter-


ing surface area, size of the  bags, and spacing between bags.

                    2
For example, 1750 ft  of filtering area can  be provided in about

     2
80 ft  of floor area by using  bags 6 in. in  diameter and 10 ft


long, and allowing 4 in. between bags.  If 12-in.-diameter bags


are used, they must be about 14 ft long to provide the same


filtering area in the same floor space, though 12-in.-diameter


bags can easily be obtained in lengths of 20 ft or more when
                             2-113

-------
there is adequate head room.   This configuration (12  in.  x 20 ft)

                                             2
would provide a baghouse having about 2500 ft  of filtering area


in the same floor space (80 ft ).     Because the length/diameter


ratio affects the stability of vertical bags, care must be taken


to ensure that bags do not rub together during operation or


cleaning.  In general the length/diameter ratio ranges from 5 to


40,   but more commonly is between 10 and 25.  Respondents in


this study indicated a range of 17 to 31 for the length/diameter


ratio.


     Design consideration must be  given to adequate space for the


collecting hopper below the filter bags.  Hoppers are commonly


designed with 45-degree or 60-degree sloping sides to provide


adequate sliding, and with some dusts a 70-degree slope is re-


quired.  Dust collected in the hopper can be removed by screw


conveyors, rotary valves, trip gates, air slides, and other


methods.


     The most common construction  material for the housing is


steel; other materials, such as concrete and aluminum, are also


used.  Corrugated asbestos cement  paneling is often used for the


exterior roofing and siding of the housing in combination with

                                       37
interior walls and partitions of steel.


Gas Conditioning or Cooling--


     Exhaust gases are often too hot to go to the baghouse immed-


iately, so they are cooled before  entering the filtration system.


Gas cooling generally is not required for kraft pulp mill power


boilers, because most are equipped with air preheaters.  Likewise


crushed stone processes do not require gas cooling.


                              2-114

-------
2.6.2  Correlations




     As stated earlier, it is difficult to establish correlations




between fabric filter design parameters and specific processes




because the fabric filters used in the various applications are




very similar.  Thus only capital and annual costs are presented




here.




2.6.3  Capital and Annual Costs of Fabric Filters




Bark/Fossil Fuel-.ired Boilers--




     Only minimal data are available to define capital and annual




costs for fabric filtration systems serving pulp mill power




boilers.  The only reliable cost information was provided by




Simpson Timber Company.  Their two fabric filters, having capa-




cities of 100,000 cfm and 130,000 acfm with a total cloth fil-




tration area of 55,315 ft , were purchased and installed at a




cost of $1.9 million in 1976.  This cost is equivalent to $8.25/




acfm or $34.35/ft2 of cloth.




     The annualized cost of operation of the two collectors could




not be isolated from other plant operation disbursements, but the




annual maintenance costs are estimated to be about $75,000.  Most




of this expense was related to bag replacement (600 bags changed



in the past year) .




Crushed Stone Industry—




     Deriving typical costs of a fabric filtration control system




in crushed stone operations is complex.  Each plant represents




unique problems in terms of materials, equipment, plant layout or




size, tonnages processed, local conditions, and air pollution






                              2-115

-------
control regulations.  In addition,  there are permanent and mobile



crushing operations.



     The capital and annual cost estimates for particulate con-



trol in the crushed stone industry  are abstracted from a recent


                                   3 8
PEDCo report prepared for U.S.  EPA.     The three control systems



considered are fabric filters,  wet  suppression system, and a com-



bination fabric filter/wet dust-suppression system.   Cost analyses



of these control systems are applied to three sizes  of model



plants:  a 200-ton/h portable plant, a 300-ton/h stationary



plant,  and a 600-ton/h stationary plant.  Costs represent retro-



fitted systems.  These model plant  sizes represent typical plant



sizes,  based on industry data,  and  corresponding control system



design and configuration.



     Installed capital costs reflect December 1977 prices.  These



costs were obtained by averaging price quotations from several


                                               39
equipment manufacturers for each system design.



     Total costs of equipment for fabric filter systems include



gas cleaning equipment, fan system,  hopper, and a screw conveyor



with an air lock.  Direct costs represent equipment  and installa-



tion costs, including foundation and support, ductwork, stack,



piping, insulation, painting, and electrical work.



     Costs of equipment for wet dust-suppression systems include



the dustsuppression equipment,  water filter and flush, high-



pressure truck-dump station, shelter house, and equipment winter-



ization.  Direct costs include equipment, foundation and supports,


                                        4 o

piping, insulation, and electrical  work.
                             2-116

-------
     Costs of other equipment for fugitive dust control are



itemized separately.  Indirect costs include engineering, con-



struction and field expenses, construction fees, startup, per-



formance test, and contingencies.  Total capital cost is the sum



of direct and indirect costs.  Contingencies and retrofit penal-


                                                   4 0
ties are included in the direct and indirect costs.



     Production losses during startup as well as research and



development costs are difficult to estimate and are not included



in the capital costs.



Bases for Annual Cost Estimates--



     Annual cost includes direct operating costs and fixed costs.



Direct operating cost components are power, water,  maintenance,



operating labor, and supplies.  Fixed cost components are pay-



roll, indirect costs, insurance, taxes, and capital recovery.



     Return on investment and product recovery credits are in-



significant and therefore are not included in annual costs.



     Several equipment manufacturers estimated the  annual costs,


                                   4 0
which reflect December 1977 prices.    Depreciation and interest



on the capital investment are computed by means of  a capital



recovery factor that is dependent on the operating  life of the



equipment and the current interest rate.  Unless otherwise



stated,  an operating life of 15 years and an annual interest rate



of 10 percent are assumed to yield a capital recovery factor of



13.2 percent of the capital costs.



     Table 2-24 presents the bases for computing annualized costs



for most cost components.
                             2-117

-------
      Table 2-24.   ANNUAL COST COMPONENTS  FOR FABRIC  FILTER
                        CONTROL SYSTEM38
     Cost component
   Basis
Direct operating costs

 Utilities
     Water
     Electricity

 Operating labor
     Direct
     Supervision

 Maintenance and supplies
     Labor and materials
     Supplies

Fixed costs

 Plant overhead, payroll,
  taxes, insurance

 Capital recovery; 15 years at
$0.25/1000 gal
$0.04/kWh
$10/man-hour
15% of direct labor
6% of capital costs
15% of labor and materials
4% of capital cost

13.2% of capital cost
Fabric Filter Control System—

     Model plant parameters—Discrete emission point-sources

(sizing and transfer operations)  controlled by fabric filtration

are conveying, packaging, screening, milling, and pulverizing

operations.

     Figure 2-18 indicates the varieties of combined exhaust flow

rates from point sources in proportion to plant capacity.  Table

2-25 presents process parameters and emission characteristics of

the three model plants.
                              2-118

-------
               1C-
           o
               TO4
                  10?
2      3    4   56789 103
 PLANT CAPACITY, tons/h
Figure 2-18.   Exhaust gas volumes  at various plant  capacities.
                                                                 39
                                 2-119

-------
  Table 2-25.  CHARACTERISTICS OF EXHAUST GAS FROM MODEL SIZING
                  AND TRANSFER OPERATIONS39/40
Plant size, tons/h
Gas flow rate, acfm
Temperature, °F
Moisture content, %
Dust loading
Inlet, gr/scf
Outlet, gr/scf
Inlet, Ib/h
Outlet, Ib/h
Cleaning efficiency, %
200
33,000
70
2

10
0.0222
2830
62
99.78
300
48,000
70
2

10
0.0222
4110
90
99.78
600
82,000
70
2

10
0.0222
7030
155
99.78
     Because of their layouts,  the plants that have capacities of

200 tons/h and 300 tons/h each require two separate fabric filters,

whereas the largest plant that has a capacity of 600 tons/h re-

quires three fabric filters.

     Design specifications for each of the fabric filters are as

follows:40

     Type:  pulsed jet,  negative pressure

     Filter velocity:  6.5 ft/min

     Filter media:  polypropylene felt bags

     Construction:  carbon steel housings

     Collection efficiency:  99.78 percent

     Pressure drop:  17  in. H_0

     Control Costs—Table 2-26 presents capital and annual costs

of fabric filter systems serving the model plants.  The total

                              2-120

-------
Table 2-26.   CAPITAL AND ANNUAL COSTS OF FABRIC FILTER SYSTEMS
          FOR MODEL SIZING AND TRANSFER OPERATIONS40

Exhaust flow rate, acfm
Number of units
CAPITAL COST
Equipment
Direct
Indirect
Capital
Total capital cost '
ANNUAL COST
Direct operating
Fixed
Total annual cost per
unit
Total annual cost
COST-EFFECTIVENESS
£/lb pollutant removed
Plant size, tons/h
200
16,500
2
$ 29,300
76,800
16,000
92,800
$186,000
$ 11,700
16,000
$ 27,700
$ 55,400
1.2
300
24,500
2
$ 38,700
101,300
19,200
120,500
$241,000
$ 15,500
20,700
$ 36,200
$ 72,400
1.1
600
27,300
2
$ 42,600
111, 900
21,300
133,200
$400,000
$ 17,800
22, 900
$ 40,700
$122,000
1.1
 Flow rate for individual sources being controlled.
 Capital cost of each unit multiplied by number of units.
 All costs escalated to December, 1977, using Chemical Engineer-
 ing Plant Index.
 Based on 2200 hours of operation per year at 75 percent of
 rated capacity.
                             2-121

-------
capital costs of retrofitting the fabric filter systems  on the
200-tons/h, 300-tons/h, and 600-tons/h model  plants  are  $186,000,
$241,000, and $400,000 respectively.   The equipment  cost repre-
sents approximately 32 percent of the total  capital  costs.  The
capital cost, expressed as cost per unit volume,  ranges  from
$4.88 to 5.64 per acfm for the large to the  small plant, as a
result of economy of scale.
     The annual costs are estimated to be $55,400,  $72,400, and
$122,000 for the small, medium, and large model plants,  respec-
tively.  These costs are based on 2200 hours  of operation per
year at 75 percent of the rated capacity.  The direct operating
costs represent about 43 percent of the total annual costs.
     Cost-effectiveness--Cost-effectiveness  does not differ
significantly for each plant size because annual costs and the
amount of pollutant removed are fairly proportional  to exhaust
volume.  The cost is computed at about l.lC/lb of pollutant re-
moved.  Figure 2-19 illustrates the variation of cost-effective-
ness with plant size.  This illustration indicates that  cost-
effectiveness will improve at some point between a 200-  to 300-
tons/h plant.  These cost estimates are applied to the model
plants only, however, and cannot be used for general estimating.
For plants of less than 200 tons/h cost could exceed 1.2C/lb
of pollutant removed.
Wet Dust-Suppression System—
     Model plant parameters—Dust emissions at critical dust-
producing points in the process flow are controlled by a wet
dust-suppression system.
                             2-122

-------
     The wet dust-suppression systems applied to each model plant


                                      40
include the following auxiliary items:



     Shelter house for pump metering mechanism



     Water filter and flush system



     System winterization



     Automatic spray at truck dump station.



     Control costs—Table 2-27 presents capital and annual costs



of the wet dust-suppression system for each  model.   Capital costs



for the 200-tons/h, 300-tons/h, and 600-tons/h model plants are



estimated at $71,000, $73,600, and $80,400,  respectively.   The



equipment costs represent about 35 percent of the total capital



costs.  Capital costs do not increase rapidly with size because



some of the equipment is identical for each  model plant.  Hence,



the cost per unit size decreases rapidly for wet dust-suppression



of a fugitive dust source.



     Annual costs are estimated at $15,000,  $16,000, and $20,100



for the 200-tons/h, 300-tons/h, and 600-tons/h model plants,



respectively.  These estimates are based on  1650 hours of  opera-



tion per year.  As shown in Table 2-27, the  direct operating



costs vary more in proportion to the plant size than do the fixed



costs.



     The cost-effectiveness of wet dust-suppression systems in-



creases rapidly with plant size.  The actual cost-effectiveness



estimate cannot be determined because no estimate of emissions is



available.
                             2-123

-------
  Table 2-27.  CAPITAL AND ANNUAL COSTS OF WET DUST-SUPPRESSION
      SYSTEMS FOR CRUSHERS, SCREENS,  TRANSFER POINTS,  AND
                         CRUSHER FEEDS40

CAPITAL COST
Equipment
Total direct cost
Total indirect cost
Total capital cost
ANN'JAL COSTb
Direct operating
Fixed
Total annual cost
Plant size, tons/h
200
$24,200
62,900
8,100
$71,000
$ 2,900
12,100
$15,000
300
$26,300
65,200
8,400
$73,600
$ 4,100
12,700
$16,800
600
$28,600
71,600
8,800
$80,400
$ 6,400
13,700
$20,100
 Includes dust-suppression equipment,  water filter and flush,
 high-pressure truck-dump station,  shelter house,  and equipment
 winterization.

 Based on 1650 hours of operation per  year.

Combined Fabric Filtration and Wet Dust-Suppression--

     Effective dust control can be achieved at some plants by

applying a combination of fabric filtration and wet dust-suppres-

sion systems.  This strategy probably  is more economical than

complete dry collection because fabric filter systems are much

more expensive.  A combined system would provide greater emission

reduction than complete wet dust-suppression.  The cost-effective-

ness would be much greater than for fabric filter systems alone.

     Model plant parameters—Fabric filters of the type previously

discussed are applied at points where  fine particle size emissions

occur in the model plants, primarily at secondary and tertiary

crushers and screens.  Wet dust-suppression techniques are used
                             2-124

-------
at primary crushers, screens, transfer points, and crusher feeds,



where particle sizes are much larger and moisture content is



higher.



     Fabric filter costs are based on estimated exhaust gas flow



rates obtained from Reference 41 for each model plant.



     Control costs—Table 2-28 presents capital and annual costs



for control by the separate and combined systems.  The total



capital  costs of the combined system for the 200-tons/h, 300-ton/h,



and 600-tons/h model plants are estimated to be $135,000, $159,000,



and $195,000, respectively.  The corresponding annual costs are



estimated to be $35,500, $43,400, and $55,500.  The capital and



annual costs are considerably lower for the combined system than



for a complete fabric filter system.  (See Table 2-26.)  The



costs increase less rapidly with plant size than with the com-



plete fabric filter control.



     Cost-effeetiveness—Because no estimate can be made of the



emission reduction achieved by the wet dust-suppression system,



its cost-effectiveness cannot be computed.  Assuming a propor-



tional increase of emissions with plant size, the cost-effective-



ness would be in ratios of about 17:14:9 for the small, medium,



and large plants,  respectively.
                              2-125

-------
     Table 2-28.   CAPITAL AND ANNUAL COSTS  OF COMBINATION
 FABRIC FILTERS AND WET DUST-SUPPRESSION SYSTEMS  FOR  CRUSHERS,
         SCREENS,  TRANSFER POINTS,  AND CRUSHER FEEDS39

A.


CAPI


ANN!'

B.
Fabric filter
Exhaust flow rate, acfm
Number of units
TAL COST
Equipment
Direct
Indirect
Total capital cost
AL COST
a
Direct operating
Fixed
Total annual costs
Wet dust suppression
CAPITAL COST


AN'N'L


Equipment
Direct
Indirect
Total capital costs
AL COST
b
Direct operating
Fixed
Total annual costs
Total combined
capital costs
Plant size, tons/h
200

11,000
1
$ 21,300
56,500
13,900
$ 70,400
$ 8,500
12,200
$ 20,700

$ 21,800
56,600
7,300
$ 63,900
S 2,900
10, 900
13,800
$134,000
300

16,500
1
S 28,300
76,800
15,000
$ 92,300
$ 11,900
15,000
$ 26,900

$ 23,700
58,700
7,600
$ 66,300
5 4,100
11,400
15,500
$159,000
600

25,000
1
$ 40,000
104,500
19,200
5124,000
$ 15,500
21,300
$ 36,800

$ 25,700
64 ,400
7,900
$ 71,300
$ 6,400
12,300
18,700
$195,000
3 Based on 2200 hours of operation per year at 75 percent of
  rated capacity.
  Based on 1650 hours of operation per year.
                             2-126

-------
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-------
                     REFERENCES  -  SECTION  2


 1.   Standards Support and  Environmental Impact  Statement -
     Volume 1:  Proposed Standards of  Performance  for Kraft Pulp
     Mills.  EPA-450/2-76-014-a.   September.  1976.

 2.   Atmospheric Emissions  from  the Pulp and Paper Manufacturing
     Industry.  EPA-450/1-73-002.   September 1973.

 3.   Environmental Pollution  Control:   Pulp  and  Paper Industry,
     Part I - Air.  EPA-625/7-76-001.   October 1976.

 4.   Weant, G.E.  Characterization of  Particulate  Emissions from
     the Stone-Processing Industry. Research Triangle  Institute,
     EPA Contract No. 68-02-0607-10.   May  1975.

 5.   Standards Support and  Environmental Impact  Statement - An
     Investigation of the Best Systems of  Emission Reduction  for
     Quarrying and Plant Process Facilities  in the Crushed and
     Broken Stone Industry.   EPA/OAQPS/RTP.   August  1975.

 6.   Particulate Pollutant  Systems Study:  Volume  III - Handbook
     of Emission Properties.   Midwest  Research Institute.  EPA
     Contract No. 22-69-104.   May  1971.

 7.   Electrostatic Precipitator  Newsletter (September 20, 1977).

 8.   Federal Register; Standards of Performance  for  New Sta-
     tionary Sources, Kraft Pulp Mills.  Part II.  September  24,
     1976.

 9.   Oglesby, S. and G.B. Nichols.  A  Manual of  Electrostatic
     Precipitator Technology, Part I:   Fundamentals.  p. 204.  PB
     196 380.  1970.

10.   Matts S. and P.O. Ohnfeldt.   Efficient  Gas  Cleaning with SF
     Electrostatic Precipitator.   Fla'kt, AB  Svenska  Flakt Fabricken,
     June 1973.

11.   Vandegrift, A.E., et al. Particulate Pollutant System
     Study, Volume III, Handbook of Emission Properties. Midwest
     Research-Institute.  Kansas City, Missouri.  1971.

12.   Marchello, J.M. and j.j. Kelly (eds.)  Gas  Cleaning for  Air
     Quality Control,  p. 219.  Marcel Dekker.   New  York.   1975.

                             2-128

-------
13.  Deutsch, W. Ann.  Physik 68.   1972.

14.  Feldman, P.L.  The Effect of Particle Size Distribution on
     the Performance of Electrostatic Precipitators.   Presented
     at the 68th Annual Meeting of APCA,  No.  74-02.3,  (June
     15-20, 1975).

15.  Myron Robinson, W. Strauss (Ed.), Electrostatic  Precipita-
     tion, in Air Pollution Control.   Volume  II.   Wiley-Inter-
     science, New York, 1972.

16.  Cooperman, P. Trans.  Am. Inst. of Elec.  Engrs. Vol.  (79)1.
     (1960).

17.  Cooperman, P., Research-Cottrell, Inc.,  In-house Report.

18.  Bump, R.L.  Precipitator Design for  Low-Odor Boilers Offer
     Special Problems.  Pulp and Paper.  1976.

19.  Oglesby, S. and G.B.  Nichols, A Manual of  Electrostatic
     Precipitator Technology, Part II: Application Area.   p. 345.
     PB 196 381.  1970.

20.  Paul, John E.  Application of ESP for Control of Fumes from
     Low-Odor Pulp Mill Recovery Boilers.   JAPCA Vol.  25, No. 2.
     1975.

21.  Cheremisinoff, P.N. and R.A.  Young,  Air  Pollution Control
     and Design Handbook.   Part I, Chapter 10.   1977.

22.  Stern, A.C.  Air Pollution.  Third Edition,  Volume IV,
     Chapter 3, p. 106.  1972.

23.  Reference 22, p. 120.

24.  Sittig,  Marshall.  Pulp and Paper Manufacturing,  Energy
     Conservation and Pollution Prevention.  p. 370.   Noyes Data
     Corp., Park Ridge, N.J.  1977.

25.  Reference 24, p. 373.

26.  Steenberg, L.R. Air Pollution Control Technology and Cost in
     Seven Selected Emission Sources.  IGCI.   EPA Contract No.
     450/3-74-060.  December 1974.

27.  Mcllvaine Wet Scrubber Manual, Volume 1, Chapter III, p. 58.

28.  Reference 27, p. 8.

29.  Reference 24, p. 373.

30.  Reference 27, p. 47.

                             2-129

-------
31.  Mcllvaine Wet Scrubber  Manual,  Volume  I, Chapter  III.

32.  Brink,  J.A.  and C.E.  Constant,  2nd,  Eng. Chem.  50 (8).

33.  Calvert,  S.D.,  Lundgren,  and  D.S. Mehta, JAPCA  22 (7),  1972,
     p. 529.

34.  Semrau, K.T.   JAPCA,  IQ_ (3)  1960, p. 200.

35.  Gorman, P.E., A.E.  Vandegift,  and L.J.  Shannon.   Fabric
     Filters in Gas Cleaning for  Air Quality Control.   Marchello,
     J.M.  and J.J. Kelly (eds.).   Marcel  Dekker,  Inc.,  New York.
     1975.

36.  McKenna,  J.D.,  J.C. Mycock,  and W.O. Lipscomb.  Applying
     Fabric  Filtration to  Coal-Firing Industrial  Boilers  - A
     Pilot Scale Investigation, EPA-650/2-74-048-a,  August 1975.

37.  Billings, C.E., and J.  Wilder.   Handbook of  Fabric Filtra-
     tion Technology,  Volume 1.   GCA Corporation.  Contract  No.
     CPA-22-69-38, December  1970.

38.  Crushed and Broken  Stone  Industry Cost Technology Guidelines
     Document (CTGD),  draft  report,  prepared by PEDCo  Environ-
     mental, Inc.  for U.S. EPA Economic Analysis  Branch,  Research
     Triangle Park,  North  Carolina.   April  1978.

39.  The Crushed Stone Industry:   Economic  Impact Analysis of
     Alternative Air Emission  Control Systems.  Arthur D.  Little,
     Inc.   EPA Contract  No.  DU-AQ-76-1349.   Final Draft.   Septem-
     ber 1975.

40.  Nonmetallic Minerals  Industries Control Equipment Costs.
     Industrial Gas Cleaning Institute, Stamford,  Connecticut,
     EPA Contract No.  68-02-1473.   February 1977.

41.  Evans,  R.J.   Methods  and  Costs of Dust Control  in Stone
     Crushing Operations.  Bureau of Mines  Information Circular
     No. 8669.  U.S. Department of the Interior.   1975.
                             2-130

-------
                            SECTION 3



    OPERATION AND MAINTENANCE OF PARTICULATE CONTROL DEVICES






     As with other complex equipment, the successful functioning



of pollution control systems depends not only on sound design



and proper installation, but also on proper operation.  Ideally,



the plant personnel who use and maintain the equipment will



understand the engineering principles on which the control



system is based and will apply this knowledge both in routine



operation/maintenance and in emergency situations.



3.1  OPERATION AND MAINTENANCE OF ELECTROSTATIC PRECIPITATORS



     This section deals specifically with electrostatic precip-



itator applications on recovery furnaces and bark/fossil fuel-



fired boilers used at kraft pulp mills.



     Problems with electrostatic precipitators can arise when the



precipitator is brought on line and also after extended operation.



Since the possible causes of poor precipitator performance are



diverse, it is impractical to outline a single procedure for



determining the nature of a specific problem.  When a malfunction



occurs, the operator must depend on his theoretical understanding



of the equipment, backed by his practical experience.  This sec-



tion of the report, therefore, provides background information on



precipitator operation, together with detailed maintenance and




trouble-shooting procedures for the major component categories.



                               3-1

-------
     Presently, two methods are used in recovery boiler operations



to concentrate the black liquor:  1} the more prevalent conven-



tional method  (direct-contact evaporation)  and 2)  the low-odor



method (indirect contact evaporation).   The nature of the parti-



culate was shown previously in Section  2.3.3, Table 2-12.



Since the basic precipitator functions  are those of charging and



collection of particles, the components and controls associated



with the transformer-rectifier (T-R) sets,  vibrators, and rappers



constitute the heart of the electrostatic precipitator system.



The more tenacious dust from the low-odor operation can be re-



moved from the precipitator plate by vibrating with air vibrators.



The collected dust from the conventional process is removed by



rapping; the trend, however, is to also use air vibrators on such



applications.



     The procedures presented here are  those suggested by Research-



Cottrell, Inc.  Although other manufacturers might recommend



different procedures as dictated by details of system design,



most of the major components, and therefore the operating pro-



cedures, are similar.  Where it is possible, the recommended



practices are interpreted in terms of their effects on equipment



performance.



3.1.1  Background on Precipitator Operation



     Electrostatic precipitation requires two groups of equip-



ment:  1) the precipitation chajnber, in which the suspended



particles are electrified and removed from the gas, and 2) the



high-voltage transformer and rectifier, which function to create



the strong electrical field in the chamber.



                              3-2

-------
     The chamber consists of an outside shell (precipitator shell)



made of metal or tile.  Suspended within the shell are grounded



steel plates  (collecting electrodes) connected to the grounded



steel framework of the supporting structure and to an earth-



driven ground.  Suspended between the plates are wires (discharge



electrodes) insulated from ground, which are negatively charged



at voltages ranging from 20,000 to 105,000 volts.  The great



difference in voltage of the wires and the collecting plates sets



up a powerful electrical field between them, which imparts a



negative charge to the solid particles suspended in the gas stream.



Understanding of this phenomenon requires some knowledge of



electricity and chemistry; for practical purposes it is enough



to know that the particles become electrically charged.  The



negatively charged particles are attracted to the collecting plates,



which are at ground potential.  The particles cling to the collect-



ing plate and become electrically inert.



     The gas that enters the precipitator laden with particles



is channeled through the precipitator outlet, while the dust



collected in the hopper or drag bottom is removed via an ash



handling system.



     It should be noted that reentrainment can be a problem in



the conventional process.  The collected dust from a conventional



process falls into a wet bottom.  The dust from the low-odor pro-



cess falls into a dry drag bottom.  The cleaning mechanism can



travel in a transverse or longitudinal direction.  Removal of the



collected dust  (principally carbon, sand, and fly-ash) from bark-
                               3-3

-------
fired and combination-fired boilers is best achieved  by  rapping



the plates and collecting the ash in trough or  pyramidal hoppers.




     Figure 3-1 illustrates the major components  of a kraft  pulp



mill precipitator with tophousing (as opposed to  insulator com-



partments) .  The dust collecting and removal system will vary



depending on the application.  Appendix B-l presents  a more



detailed explanation of precipitator operations including subsys-



tems and components such as transformer-rectifiers, rappers,



vibrators, the upper precipitator,  discharge wires, collecting



plates, and the lower precipitator.  The following  section



describes the fundamental operational procedures  necessary for



routine operation.



3.1.2  Precipitator Startup and Shutdown Procedures



     Operation of an electrostatic  precipitator involves high



voltage, which is dangerous to life.  Although  all  practical



safety measures are incorporated into the unit, extreme  caution



should be exercised at all times.  An electrostatic precipitator



is, in effect, a large capacitor which, when de-energized, can



retain dangerous electric charges.   Therefore,  grounding mech-



anisms provided at each access point should be  used before



entering the precipitator.



Preoperation Checklist--



     Before placing the equipment in operation, plant personnel



should perform a thorough check and visually inspect  the system



components in accordance with recommendations of  the  manufacturer.



A complete checklist of items is presented in Appendix B-2.   Some



of the major items that should be checked are summarized below:;



                               3-4

-------
                                       GROUND SWITCH BOX-
                                         ON TRANSFORMER
         TRANSFORMER-
         RECTIFIER
HEAT JACKET
PERFORATED-
DISTRIBUTION
PLATES
 DISCHARGE
 ELECTRODE
                                                    DISCHARGE
                                                    ELECTRODE
                                                    VIBRATOR
                                                      COLLECTING
                                                      ELECTRODE
                                                      RAPPERS
                                                                       TOP HOUSING
                                                                       ACCESS DOOR
                                                                        TOP HOUSING
                                                                        HOT ROOF
                                                            ACCESS  DOOR
                                                            BETWEEN
                                                            COLLECTING
                                                            PLATE SECTIONS
                                                      COLLECTING ELECTRODES
                                          WET BOTTOM
Figure 3-1.
                          Uet bottom electrostatic precipitator
                             with heat  jacket.
                                      3-5

-------
     Control unit

     Proper connections to controls

     Silicon rectifier unit

     Rectifier-transformer insulating liquid level
     Rectifier ground switch operation
     Rectifier high-voltage connections
     High-voltage bus transfer switch operation

     High-tension connection

     High-tension bus duct
     Proper installation
     Vent ports properly installed

     Equipment grounding

     Frecipitator grounded
     Transformer grounded
     Rectifier controls grounded
     High-tension guard grounded
     Conduits grounded
     Rapper and vibrator ground jumpers in place

Air Load Test--

     After the precipitator is inspected (i.e., preoperational

check adjustment of the rectifier control and check of safety

features), the air load test is performed.  Air load is defined

as energization of the precipitator with minimum flow of air (stack

draft)  through the precipitator.  Before introduction of an air

load or gas load  (i.e., entrance of dust-laden gas into the pre-

cipitator), the following components should be energized:

     Collecting plate vibrator-rappers
     Perforated distribution plate rappers  {if present)
     High-tension discharge electrode vibrators
     Bushing heaters; housing/compartments
     Hopper heaters;  vibrators; level indicators
     Transformer rectifier (T-R)
     Rectifier control units
     Ventilation ar.d  forced-draft fans
     Dust-conveyir.g system
                              3-6

-------
     The purpose of the air load test is to establish reference



readings for future operations, to check operation of electrical



equipment, and to detect any improper wire clearances or grounds



not detected during preoperation inspection.  Air load data are



taken with the internal metal surfaces clean.  The data consist



of current-voltage characteristics at intervals of roughly 10



percent of the T-R milliamp rating, gas flow rate, gas tempera-



ture, and relative humidity.



     For an air load test the precipitator is energized on manual



control.  The electrical characteristics of a precipitator are



such that no sparking should occur.  If sparking does occur, an



internal inspection must be made to determine the cause.  Usually,



the causes are close electrical clearances and foreign matter,



such as baling wire, that has been left inside the precipitator.



     After the precipitator has been in operation for some time,



it may be necessary to shut it down to perform an internal inspec-



tion.  At such times it is of interest to take air load data for



comparison with the original readings.



Gas Load Test—



     The operation of a precipitator on gas load differs con-



siderably from operation on air load with respect to voltage and



current relationships.  High current and low voltage charac-



terize the air load test, whereas low current and high voltage



characterize the gas load test.  These relationships govern



operation of the precipitator and the final setting of the



electrical equipment.
                              3-7

-------
     In general, optimum precipitator efficiencies are obtained



when the dc voltage applied to the precipitator  is at the thresh-



old of sparking.  The spark rate at this point will be on the



order of 50 to 150 sparks per minute and may be  controlled at



this level with automatic control.




Shutdown Procedure--



     To shut down the precipitator, the operator opens the con-



trol circuit start/stop switch and then opens the main circuit



breaker.  Before entering the system, the operator should follow



all safety procedures.   Proper grounding of  all  precipitator



parts is important.  The key interlock system prevents access to



the interior of each T-R ground switch enclosure until the in-



dividual set is de-energized and the ground  connections are made.



This system prevents access to the interior  of the precipitator,



including top housing or insulator compartments, precipitator



roof doors, side doors, and hopper doors, until  the T-R's of each



precipitator are de-energized and ground connections are made.



Purging the system with ambient air may also be  desirable from



the standpoint of plant personnel who must inspect the internal



parts of the precipitator.



3.1.3  Inspection and Maintenance During Normal^ Operation




     Appendix B-3 consists of detailed directions for plant per-



sonnel who are assigned responsibility for inspection and main-



tenance of precipitator systems.  These instructions, abstracted




from Research-Cottrel1's suggested operation and maintenance



procedures, are representative of the level  of inspection and






                               3-8

-------
maintenance required for successful precipitator operation with

minimum downtime.  Although electrical portions of a precipitator

require very little maintenance, the items enumerated in Appendix

B-3 should be attended regularly if the equipment is to give

optimum service.  It is considered good practice to assign one

plant operator on each shift the task of checking and recording

data on electrical equipment at the start'of the shift.

     The cycle or inspection and maintenance during normal

operation includes the following components:

     T-R sets and associated equipment and controls
     Transformer enclosure
     Pipe and guard
     Vibrators
     Plate rappers
     Top housing
     Insulator compartments
     Upper high tension frame
     Discharge wires
     Collecting plates
     Lower precipitator steadying frame
     Dust collection point (dry or wet bottom)
     Hoppers and screw conveyors
     Precipitator shell.

Maintenance Schedule and Troubleshooting—

     Appendix B-4 also presents a detailed list of maintenance

procedures that should be performed on a daily, weekly, monthly,

quarterly, semi-annual, and annual basis.  These procedures

typify the level of effort required to maintain optimum operation.

For example, the annual inspection covers the following conditions

and subsystems:
                               3-9

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-------
     Dust accumulation
     Discharge wires
     Alignment of plates and wires
     High-tension and plate vibrator-rappers
     High-tension frame support bushing
     High-voltage electrical control  cabinet
     T-R sets
     Dry/wet bottom
     Hoppers
     Screw conveyor

Table B-3-1, Appendix B-4, lists troubleshooting measures recom-

mended by precipitator manufacturers  for determining the most

probable cause of precipitator problems; Table B-3-2 gives ar.

example of the frequency of failure and time to repair various

components of a typical industrial precipitator.

3.1.4  Op e r a 1 1 on a .-. d M a i n t_e_n a n c e Problems Specific to Kraft
       P^lp" "Mill's"                                          "
     The information presented in the preceding sections pertains

to most precipitator applications.  Table 3-1 illustrates the

important differences between utility and kraft pulp mill precip-

itators, i.e., those controlling recovery furnaces and bark-fired

and combination-fired boilers.  The most common malfunctions

associated with electrostatic precipi ta tors applied to recovery

furnaces stem from corrosion and failure of rappers.  Other prob-

lems result from drag bottom conveyors, plugging of the inlet

distribution plate,  buildup on ladder vanes, and "snowing"

(intermittent puffing of recovery furnace stacks).

Corrosion--

     Corrosion is more severe with conventional than with low-odor

recovery furnace operations, mainly because of the lower operating

gas temperatures in conventional recovery furnaces.  It is
                               3-12

-------
essential that both the precipitator inlet and outlet flues be



insulated, as well as the shell.  At flue gas temperatures below



300°F, local cold spots may cause condensation and create severe



corrosion.  A heated steam or air coil system provides a means of



keeping all internal shell wall surfaces above the dew point of



vapors in the gas being cleaned and thus preventing condensation



of corrosive chemicals anywhere on the walls.  Operating the wet



bottom at extremely low liquor levels leads to inleakage of cold



outside air at the agitator hubs, which causes corrosion of the



wet pan.  Maintaining the proper liquor level can eliminate this



problem.



Rapper Failure--



     Dust is removed from the collecting and discharge electrodes



by means of air or electrically operated vibrators/rappers.  Al-



though intensities and frequencies depend on the specific installa-



tion, plate and wire vibrators and rappers are usually in con-



tinuous operation.  The importance of the vibrating/rapping system



cannot be overemphasized, since any failures within the system will



cause loss of power input to the precipitator and a reduction in



precipitator performance.



Drag Bottom Conveyors—



     Dust is conveyed from the electrostatic precipitator dust



chamber to the salt-cake mix tank either concurrently to the gas



flow  (longitudinal drag bottom) or perpendicularly to the gas



flow  (transverse drag bottom).  The latter method lessens the



possibility of gas sneakage, which is typically associated with
                              3-13

-------
the longitudinal drag bottom.   Systems that convey the dust per-




pendicular to the gas flow must be broken into at least two




sections.  One conveyor mechanism should serve the inlet field




separately and should be designed to accommodate the bulk of the




dust.




Plugging of Inlet Distribution Plate and Ladder Vanes--




     Plugging is a function of operating temperature.   Most prob-




lems are eliminated when operating temperature exceeds 3258F.




Dust accumulations on the inlet turning vanes cause some maldis-




tribution of gas flow patterns.  Any change in design to eliminate




the necessity cf these structures would improve the operation,




rair.ter.ar.ee, and performance of the precipitator.




"Snowing"—




     The principal cause of "snowing" is dust-laden gases bypass-




ing the treatment zones.  In wet bottom units the gases pass




through gaps between the baffle plates and tile shell.  Other




causes of "snowing" can be a sudden release of particles accumu-



lated in the ductwork, too heavy vibrating or rapping, too high




gas velocities,  and an increase in load on the precipitator




caused by ar. increase in throughput of the recovery furnace.  Use




of a low-energy scrubber following an electrostatic precipitator




helps to eliminate "snowing."




     A 1974 survey by the TC-1 corrj?ittee of the Air Pollution




Control Association  (APCA) details operational problems of 36




paper mills reporting on 49 precipitators.   Respondents indicated




that rapper/vibrators presented the largest maintenance problem
                             3-14

-------
followed by discharge electrodes, collecting plates, insulators


and dust removal system.  Table 3-2 compares maintenance problems


for utility, metallurgical, and paper mill applications from the


above study.  Paper mill respondents reported maintenance to be


a greater problem in general, than did utilities or respondents


from metallurgical processes.


     The incidence of maintenance problems as reported by paper


mills corresponds well to the design and operational information


presented in Table 3-1 on kraft recovery boilers.


     Little information is available concerning malfunctions


associated with bark-fired combination-fired boilers.  One pos-


sible source of problems with such an application is the potential


for fire caused by buildup of "char" on precipitator walls and


especially in the hoppers.  The fire hazard can be minimized by


installing trough type hoppers for continuous removal of dust.


Also the elimination of all inleakage will decrease the avail-


ability of air for combustion.


3.2  MAINTENANCE AND OPERATION OF MECHANICAL COLLECTORS SERVICING
     BARK/FOSSIL-FUEL BOILERS


     Mechanical cyclone collectors are used as primary collectors


on wood-fired boilers or as first-stage collectors for coal-

            4
fired units.


     Mechanical collectors separate dust from a gas stream by a


combination of centrifugal, gravitational, and inertial forces.


Cyclones, the most common of the mechanical collectors, make use


of most of these mechanical forces.  Rotational action creates a


centrifugal force that drives the suspended particles to the



                               3-15

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wall of the cylinder.  The gas and the dust begin a downward



spiral towards the cone and finally to the dust discharge; this



outside downward spiral is the main vortex.  As the main vortex



spirals downward, a quantity of gas is drawn radially inward to



feed a smaller inner vortex spiralling upwards to the clean gas



discharge tube.



3.2.1  Startup/Shutdown                    ;



     Check blower rotation.



     Make sure that all inspection doors, connections, etc., are



closed.



     Turn on blower and check current, pressure drop, and system



pressure drop.



     Check inlet and outlet gas and dust flows.  To shut the



system down, pass clean air through the system to permit the cy-



clone to dry and empty out, then turn off blower.



     Clean out the hoppers to prevent plugging.



3.2.2  Normal Operation



     At least once a shift, the pressure drop across the collec-



tor should be recorded.  Normally, the pressure drop across the



cyclone is greater than that of any other component in the sys-



tem.  If the pressure drop is measured across the system and if



resistance to gas flow occurs somewhere other than in the cy-



clone, the reduction of gas flow could reduce the pressure drop



across the cyclone.  It is advisable to install a manometer



across the fan and record static pressure readings from the time



of startup.   These are used as a reference for subsequent opera-



tions.




                              3-17

-------
     Every collector should be equipped with a test tap at the



inlet and outlet ducts to monitor pressure drop across the unit.



The dust discharge hopper should always be equipped with a poke-



hole on the top surface.   The ash removal system is operated



frequently enough to ensure that the hopper never fills enough to



reach the bottom of the collecting tube.  If there is any doubt



about this, install a bin level gauge with an alarm.  Leakage



will reduce efficiency.




^ • 2 • ^  .Maintenance



     Leakage into the cyclone or dust discharge hopper is diffi-



cult to detect on a negative pressure system.  When a rotary



valve acts as the seal, the wear plate should be self-adjusting



so that as it wears down (metal on metal) it always maintains a



seal.  When a counterweighted or flap valve acts as the seal, the



maintenance crew must check for buildup in the valve seat or



flapper plate.



     Additional checks should be made on fan bearings, leakage



around gaskets and valves,  and general wear and tear on the



system.



3.2.4  Operation an_d_ Maintenance Problems Specific to Cyclones



     Literature regarding bark boiler operations is so scarce



that most of the design considerations for cyclones are presented



in general terms.  Where information specific to bark bcilers is



available, it is included together with some typical problems of




cyclone operation.
                               3-18

-------
     The action inside a cyclone is always dynamic; the dust



particles are either gouging and channeling or sticking to a sur-



face and then to each other, all of which can cause erosion and



dust buildup.



Erosion—



     Particles with high specific gravity, and in high concentra-



tion, moving at high velocities and impinging on a surface will



erode the cyclone wall.  With light inlet dust loadings, erosion



is prevalent in the cone; with heavier inlet dust loadings, ero-



sion occurs in the cylinder of the cyclone.  Improper cyclone



design or poor operating conditions tend to concentrate the fast-



moving dust and increase erosion.   The areas most prone to



erosion damage are weld seams, mismatched flange seams, the



bottom of the cone, and the wall opposite the inlet.  Erosion can



be eliminated by installing removable wear plates of abrasion-



resistant metal or rubber.  Erosion can be reduced by increasing



the diameter of the cyclone body without increasing the diameter



of the gas outlet tube.  This can lead to an increase in pressure



drop.   The use of troweled or cast refractory linings is the best



method of combating erosion in cyclones.



Dust Buildup—



     Plugging of the cyclone reduces efficiency and increases



pressure drop, and may increase erosion.  Dust buildup usually



occurs at the dust outlet or at the cyclone wall.  Dust outlets
                              3-19

-------
become plugged by foreign matter or by hoppers overfilling.


Buildup on the cyclone wall is a function of particle size and


caking characteristics.  The presence of fine dust such as that


from salt emissions from bark boilers and moisture condensing on


the walls tend to increase dust buildup.  Maintaining gas veloc-


ities above 50 ft/s will minimize buildup on the cyclone wall by


the scouring action of the gas.


3.3  OPERATION AND MAINTENANCE OF WET SCRUBBERS


     In the kraft pulp mill industry wet scrubbers are used on


sludge lime kilns, smelt dissolving tanks,  and bark/fossil-fuel


boilers.


     Historically, dry mechanical collectors and low-energy


scrubbers v.ere used to control dust emissions from the crushed


stone industry.  Presently, the controls used most commonly are


fabric filters, followed in order by wet suppression techniques,


a combination of wet dust suppression and fabric filters, and

                                           g
mechanical collectors and/or wet scrubbers.   In stone crushing


operations the most co.T.nonly used wet scrubber is the venturi.


For this reason, the following commentary is restricted to gas


atc-ized spray type scrubbers.


3.3.1  Description


     Gas atomized spray type scrubbers utilize a moving gas


stream to atomize liquid into drops and then accelerate the


drops.  Acceleration of the gas provides impaction forces as well


as intimate contact with the liquid stream.   Within this category


many differences in design and operation may be noted with re-
                              3-20

-------
spect to the following items: method of adjusting pressure drop



(the difference being that between the true venturi and the



annular orifice); the method of moisture elimination (centrifugal



moisture elimination, as with spinning vanes or multi centri-



fugals).  In any event, most gas atomized spray scrubbers incor-



porate the converging and diverging section typical of the ven-



turi throat.




     The collection efficiency of a venturi scrubber is dependent



upon the pressure drop across the scrubber.  Pressure drop in



turn is dependent upon operation at close to design flow condi-



tions or provision of an adjustable venturi throat.  The low flue



gas temperature and high moisture content of the flue gases from



a venturi scrubber may lead to undesirable plume rise and plume



visibility.  The scrubbing medium may affect the odorous emis-




sions, and fresh water rather than contaminated condensate should



be used to minimize odorous emissions.  Venturi scrubbers that



incorporate variable throat designs provide a high level of



efficiency under varying inlet conditions when operated within



their design capacity.



     A typical flooded-disc scrubber system for particulate col-



lection consists of a flooded-disc scrubber, a mist eliminator



with sump, two recirculation pumps, and one booster fan or ID



fan.  A gas prequencher is sometimes required for treating high-



temperature gas.



     The flooded disc scrubber, shown in Figure 3-2, is composed



of a disc in the tapered throat section of a vertical hollow
                              3-21

-------
        -"*• ~v^W~ i '" T?^~  i 5-"i -
Figure  3-2.   ^.esearch-Cottrell flooded  di
sc scrubber.,
                          3-22

-------
cylinder.  The disc is supported by a pipe, and an open annulus



is formed between the wall and the disc.  As the gas flows



through the annulus and the scrubbing water is ejected simultane-



ously across the disc face, atomization takes place at the an-



nulus.  The millions of fine water droplets that are created are



used for particle capture in the gas stream.  The particulate



collection efficiency of the scrubber depends on the degree of



atomization, which is indicated by the pressure drop across the



scrubber.  Pressure drop across the scrubber can be regulated by



controlling the vertical displacement of the disc in the venturi



throat section automatically or manually.  To provide the same



collection efficiency, the pressure drop must be higher in col-



lecting fine particles than in collecting coarse ones.  Given



particles of the same size, the pressure drop must be higher to



achieve relatively higher collection efficiency.



     The purpose of the mist eliminator is to separate the dust-



laden water droplets from the gas stream by centrifugal force.



The separated dust-laden water flows by gravity to a sump for re-



circulation to the scrubber.  The solids content of the slurry



that is recirculated by the recycle pump gradually increases.



For control of the solids content level in the slurry, a purge



stream from the discharge of the recycle pump is pumped out of



the system, as indicated by the slurry density control.  During



system operation, some water is lost from the sump with the



purged slurry and some is vaporized as the hot gas comes in



contact with the scrubbing liquor.  To compensate for the lost
                               3-23

-------
water, a makeup water stream is pumped to the recirculation sump,

as indicated by the slurry level control.

     All of the variables are controlled within the high and low

limits.  An alarm signals any operating condition beyond the con-

trol limits to warn the operator of an abnormal condition.   The

m.a;cr controls and alarms in the scrubber system include pressure

drop across the scrubber, slurry density in the scrubber, slurry

level cf the recirculation sump, and slurry flow rate to the

scrubber.  For the purpose of safety,  the scrubber system should

incorporate interlock circuits to protect the equipment in  the

event cf an emergency.

3.3.2  Operation

Freooeration—

     Before the system startup, all major items of equipment,

connecting pipes, and auxiliaries must be inspected, cleaned, and

tested.  A new system should be checked for leaks and instabili-

ties by an air test for the fans and ductworks and a hydraulic

test for pipings and valves.  In addition, a water test should be

cerformed to ensure that equipment, instruments, and control >'

safety systems are working properly.  The items that should be

checked in preoperation tests are summarized below:

     °    FD/ID fan

          Electrical controls, fan bearing coolant system,  align-
          ment, lubrication, vibration sensors, bearing tempera-
          ture sensors.
                               3-24

-------
     0    Pumps

          Belt tension, pump rotation, pump alignment, lubrica-
          tion, seal water, packing, pressure gauge, suction and
          discharge valves, motor bearing temperature, hydraulic
          system (for flooded-disc control pump).

     °    Control Systems

          Flue gas bypass, pressure drop, makeup water rate, re-
          circulation sump level, slurry density,  slurry purge
          rate.

     °    Safety Systems  (interlocks and alarms)

          High flue gas pressure, low level in sump, high and low
          density.

     °    Utilities

          Electric power, instrumentation air, process water,
          process return water.

Startup--

     To start up a system for the actual operation or for a water

test operation, one must follow the procedure described in the

system designer's operating manual.  Following are several steps

in the startup of a new scrubber system:

     1.   Close all drain valves.

     2.   Turn on circuit breakers for all instruments and elec-
          tric valves.

     3.   Set all monitoring instruments at zero reading.

     4.   Startup the service water system and raise the water
          level in the sump to the designated level.

     5.   Turn on the recycle pumps circuit breakers and start up
          the operating and standby pumps.

     6.   Turn on the circuit breaker for the disc control pump,
          start up the disc control pump, and adjust the high and
          low limits of the pressure drop indicator (in venturi
          scrubbers) .
                               3-25

-------
     7.   Close the flue gas bypass dampers and start the fan.

     8.   Check the scrubber pressure controller and the system
          monitoring ir.struments.

Shutdown--

     Following is a general procedure for planned shutdown of a

flooded disc scrubber system:

     1.   Turn the flue gas damper to the bypass position and
          stop the fan.

     2.   Close the makeup water and slurry couple valves.

     3.   Stop the recycle pumps (both operating and standby).

     4.   Open the drain valves at the slurry pumping lir.es and
          flush the lir.es, gauges,  and p_L.-.ps with water.

     5.   Stop the disc control pump and leave the disc in the
          fully raised position.

     6.   Open the drain line on the pressure gauges to the
          throat and disc and allow the line to drain.

Ncrr.al Operation-

     L'nder normal operating conditions, all of the control param-

eters should be held within the defined ranges.  These include

the scrubber pressure drop, recycle pur.p rate, makeup water rate,

slurry density, slurry purge rate,  and recirculation sump level.

     An abnormal condition is defined as a deviation of the

operating condition beyond the normal range.  The abnormal con-

dition will be indicated by an alarm.  If the operator cannot

correct the condition, under certain circumstances an interlock

will open the flue gas bypass damper and shut down the scrubber

system.

     During normal operations the following malfunctions may

develop:


                              3-26

-------
     1.   Pump impeller wear is indicated by a reduction in
          scrubber recycle flow.   Valve or nozzle erosion is
          indicated by an increase in scrubber recycle flow.

     2.   A decrease in scrubber bleed flow is associated with
          line plugging.  An increase in bleed flow can indicate
          a worn valve.

     3.   An increase in pressure drop can be caused by plugging
          of packing or by an increase in flow of gas or liquor.

     4.   An increase in pump discharge pressure at proper flow
          rate usually indicates line plugging.

     5.   Fan inlet and outlet pressure readings can be used to
          check flow as well as damper setting.

     6.   Dust buildup on fan blades is indicated by an increase
          in fan vibration.

     7.   Motor current indicates whether a flow decrease is
          caused by impeller wear, plugging, or an incorrect flow
          meter setting.  Fan current is synonymous with gas
          throughput.

     The following alarm conditions are associated with the

system:

     1.   Scrubber pressure  drop

          An alarm condition may occur because of a malfunction-
          ing pressure drop  controller, failure of the disc
          control pump, jammed disc, or a rapid change of boiler
          load.

     2.   Slurry density

          An alarm condition may occur because of a malfunction-
          ing control, a defect in the density control valve, a
          malfunction in the sump level control, or a change in
          the makeup water rate.

     3.   Recirculation sump level

          An alarm condition may occur because of a malfunction-
          ing control or because of high or low level of slurry
          in the sump.
                             3-27

-------
     4.   Others

          An alarm condition may occur because of plugged lines,
          closed valves,  pump trouble, or fan trouble.

3.3.3  Inspection and ^jJ\t_e_n_ajT_ce__Du_ring Normal Operation

     Many of the items on the preoperation checklist should be

checked in routine maintenance.   This maintenance generally in-

cludes unplugging lines,  nozzles, pumps, etc.; replacing worn

equipment parts, erosion/corrosion prevention liners, and instru-

ments  (level indicators,  density indicators, etc.);  and repairing

damaged components when this is practical from the standpoint of

labor and materials.

     The wet-dry line must be inspected periodically for buildup

of solids.  Spray nozzles and liquid inlets must be checked to

see that they are open and distributing the liquid properly.

Corrosion can occur underneath built-up scale.  Abrasion is

another ma^or problem in most scrubbers with mechanical or cen-

trifugal shaft actuation devices.

     Points of possible corrosion and abrasion must be inspected

frequently.  These include throats, orifices, elbows, and any

other high-wear areas.  Wear on coatings and metal surfaces

should be repaired as needed.  Ductwork, dampers, fans, centri-

fugal pumps, valves, and piping require systematic inspection.

     Most fan problems are indicated by a change in vibration.

When a fan is inspected,  the casing should be opened and the

wheel and casing washed.   The wheel can be checked for erosion,

pitting, and cracking, particularly in weld areas.  Many fan
                              3-28

-------
problems are caused by lack of proper bearing lubrication.   If

the fan is equipped with a spray wash system, the piping and

nozzles should be thoroughly inspected.   Unusual stresses in the

fan can tear spray piping loose and cause chipping of the fan

wheel.

     Centrifugal pumps should be opened  periodically and in-

spected.  Pump packing should be replaced during each inspection.

The liquid level to the pump gland (packed type) should be  checked

once per shift to prevent corrosive or erosive damage of the

shaft, sleeve, and bearing.

     The following checklist, based on problems encountered in

scrubber operation, should be followed routinely.  Corrections

should be in accordance with the manufacturers' recommended pro-

cedures.

     0    Check the scrubber disc in the venturi scrubber to
          ensure even distribution across the disc surface.

     0    Check erosion and corrosion of all scrubber internal
          surfaces.  Repair as necessary.

     0    Clean and descale all scrubber internal surfaces.
          While descaling, exercise care to prevent damage  to the
          linings.

     °    Perform maintenance of the hydraulic packing of the
          scrubber disc.

     0    Check nozzles for buildup or damage.  Repair or replace
          as necessary.

     0    Check for solids buildup in blowdown lines.  The  lines
          may be cleaned without system shutdown, and a flush
          connection may be installed to prevent further buildup.

     0    Check for corrosion, erosion,  and leaks in lines  having
          protective liners, which may have deteriorated.  Replace
          liners as required.


                               3-29

-------
     •     Check operation  of  mist  eliminator.  Formation of
          droplets can be  caused by  excessive  gas  flow  rate,
          plugged drains  from the  moisture  eliminator,  or  con-
          densation in the outlet  duct.

     0     Check pumps for  wear,  seal water,  packing,  and smooth
          operation.

     0     Check dampers and damper linkages  for  proper  position-
          ing and wear.

     0     Check fans for  lubrication,  fan bearing  coolant, belt
          wear and belt tension, and erosion/corrosion  of  the
          impeller.

     0     Inspect all interior surfaces  and  condition of rist
          eliminator and  sump during major  outages.

     0     Inspect the exterior for leaks in  all  process and
          control lines,  ductwork, and expansion joints.

     0     Note the condition  of  all  instruments  such  as level
          probes and density  prcbes  with regard  to solids  build-
          up.  It is impractical and usually impossible to remove
          solids buildup  from the  probes, which  often must be
          replaced.

     0     Perform, a final  check  for  proper  operation  of density
          sensors, pressure drop control, and  level elements.

     0     In the impingement  scrubber, check the liquid level
          control and possible solids deposition in the cone
          bottom.

     Table 3-3 lists general  maintenance requirer er.ts fcr  venturi

scrubbers based on two ranges of pressure drops, and  various

lining  materials and gas  characteristics.   This  table should  be

useful  in the selection cf scrubber  liners  for lime kilns, smelt

dissolving tanks, combination bark/fossil-fuel boilers, and

various crushed stone processes.

Spare Parts—

     The minimum inventory is one  of each part for each venturi

scrubber.  The inventory for  a venturi system is given  in Table

3-4.9
                              3-30

-------
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3-32

-------
Manpower Requirements--


     Table 3-5 presents general manpower requirements for main-


tenance involving scaling and plugging for both the wet approach


and liquid injection type venturi scrubbers.  The preceding dis-


cussion has given an indication of maintenance items, maintenance


times, and spare parts inventory for a venturi scrubber system.


Table 3-6 completes this picture by presenting the types of per-


sonnel generally required to perform maintenance on various parts

                               9
of the venturi scrubber system.


   Table 3-5.  MANPOWER REQUIREMENTS FOR MAINTENANCE^INVOLVING
            PLUGGING AND SCALING OF VENTURI SCRUBBER
Type of
venturi
scrubber
Wet
approach
Liquid
injection
Type of problem
Plugging
Mechanical
cleaners
1 man/shift/
mo
1 man/shift/
mo
Cylinder
cleaners
1 man/shift/
mo
1 man/shift/
mo
Scaling
Chemical
cleaning
3 men/shift/
wk
3 men/shift/
wk
Hand
cleaning
1 man/shift/
wk
1 man/shift/
wk
                              3-33

-------
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                                         3-34

-------
3.4  OPERATION AND MAINTENANCE OF FABRIC FILTERS



3.4.1  Background Information on Fabric Filter Operation



     A fabric filter baghouse consists of a large metal box



divided into two chambers of plenums, one for dirty air and one



for clean air.  Rows of fabric bags form a partition or interface



between the plenums.  A polluted gas stream is ducted into the



dirty-air plenum, where it is distributed evenly to the bags.



The gas passes through the bags, enters the clean-air plenum, and



is exhausted into the atmosphere through a stack.



     Upon startup of a baghouse with new bags some stack emis-



sions are usually visible.  This is because the bag fabric, which



is the filtering medium, is porous and some of the fine particu-



late passes through the interstices between the fibers.  After a



short time, however, a dust cake builds up on the surface of the



bags and becomes the actual filtering medium.  The bags then act



as a matrix to support the dust cake.



     Buildup of the dust cake is desirable until the system



reaches a certain pressure drop, at which point the bags must be



cleaned.  Improper cleaning will cause the pressure drop to



increase; if it becomes high enough, particles of dust may be



forced into the bag filter, causing the bags to become "blinded."



When this happens, air flow is restricted and the bags may have



to be replaced or removed and cleaned to restore proper operating



capacity.  In addition to the costs of replacement and cleaning,



high pressure-drop increases the cost of moving air through the



system.






                              3-35

-------
     A typical reverse-air or shaker-type baghouse is shown in




Figure 3-3, and a pulse type baghouse is presented in Figure




3-4.  Operation of the various types of cleaning mechanisms is




discussed below.




Shake;  Many mechanical shaking methods are in use.   Most com-




monly, bags are shaken from the upper fastening.  Several com-




binations of horizontal and vertical motion can be used.   The




bags -ay all be fastened to a common framework moving horizon-




tally or the frame may have slight additional upward or downward




swing, depending on the linkage holding the framework.  The




framework can also be oscillated vertically.




     During the shake, the filtering should be stopped.  Other-




wise, the dust will work through the cloth, reducing the effi-




ciency and possibly damaging the cloth by internal abrasion.  An




effective cleaning method involves a series of alternate flows




and shakes.  This motion provides a gentle treatment of the




cloth, and the cleaning is uniform and thorough.




     In a typical cycle, the inlet flow to the compartment is




first dar.pered off by a timer.  If necessary, the outlet vent is




also closed  (Figure 3-5).  In the absence of an air lock between




adjacent hoppers, it may be necessary to close a damper to pre-




vent the intrusion of dirty air from hoppers still operating.




There should be zero forward pressure across the fabric during




shaking, since otherwise dust will work through the fabric.  The




timer starts the shaker motor, and the bags are shaken.  Shaking




continues for about 10 to 50 cycles, each cycle taking about 0.2






                              3-36

-------
SHAKER
MOTOR
                           »£nSEI2I33HL£.,-  -J££
                                                      TLEAN AIR
    Figure 3-3.   Reverse  air or  shaker  type
                        3-37

-------
                                     COMPRESSED AIR
Figure  3-4.   Pulse  jet type,
              3-38

-------
to 1 second.  Then the timer may start a slight flow of clean



reverse air using an auxiliary blower for 10 to 20 seconds.  The



shaking may be repeated, this time during the reverse flow.



Finally, the cleaning is stopped and after a pause to allow the



dust to settle, the inlet and outlet dampers are opened and the



compartment resumes filtering.  The entire cleaning cycle may



take from 30 seconds to a few minutes.  Some installations do not



return the compartment on line until the next one is ready to be



cleaned, thereby achieving a fairly steady overall flow through



the baghouse system at the expense of some over-capacity.



Reverse Flow;  If the dust can be released fairly easily from the



fabric, a low-pressure reversal of the flow may be enough to



loosen the cake without mechanical agitation.  To minimize flex-



ural attrition of the fabric, it is supported by a metal grid,



mesh, or rings and is usally kept under some tension.  The sup-



port is usually on the clean side of the tube or bag, although



dirty-side support can help to keep the sides of the bag or the



panels far enough apart to allow the cake to fall to the hopper.



     Flow reversal is achieved in several ways.  In addition to



the standard dampers on each compartment, each one can have its



own reversing fan.  A few models have a traveling apparatus that



goes from bag to bag or from panel to panel, blocking off the



primary flow and introducing some air in the reverse direction



with a secondary blower.  A simpler method is to take advantage



of suction on the dirty side or of relative pressure on the clean



side without using another blower, as shown in Figure 3-6.






                              3-39

-------
        I~~I
       \
               FILTERING
                                                  TLET S^JT
                            INLET SHUT
Figure 3-5.   Diagran  shewing  norral  operation and shake
             cleaning  of  a  fabric  filter.10
                        3-40

-------
     Any flow volume reversed through the filter must be refil-



tered.  Therefore in addition to taking cloth out of the system



for cleaning, this cleaning method increases the total air flow



in the remainder of the system.  The net increase in air/cloth



ratio is normally 10 percent or less.



Plenum Pulse;  This method is intended to overcome some of the



difficulties associated with other methods of cleaning.  In




plenum pulse equipment a sharp pulse of compressed air is re-



leased in the plenum chamber, giving rise to some combination of



shock, fabric deformation, and flow reversal.  The result is the



removal of the dust deposit with only a brief interruption of the



filtering flow.  The fabric receives a minimum of flexural wear,



and the filter installation is smaller because the fabric is in



use practically all the time.




     The main distinction of pulsed equipment is the brief clean-



ing time, typically around 0.1 second.  Because of the very low



ratio of cleaning time to filtering time, pulsed equipment is



especially useful with heavy dust loadings.



Pulsed Jet;  This cleaning method is similar to plenum pulse



cleaning.  The difference is that in pulse jet cleaning each bag



is individually pulsed, whereas in plenum pulse cleaning the



whole compartment of bags is pulsed by introduction of pulsing



air in the plenum chamber.
                              3-41

-------
                                           OPTIONAL, TO AVOID
                                           TEMPERATURE CHANGES
                                                «	,
                                                      I
                                                    PRESSURE
             F:

             R:
COMPARTMENTS FILTERING
   ;ARTMENT BEING  CLEANED EY  DA-PERED
CONTROL FRDM SUCTION SIDE OF  SYSTEM
Figure  3-6.   Schematic for  reverse  flow cleaning during
              continuous  filter operation.1°
                          3-42

-------
Vibration or Rapping;  This method of cleaning is particularly

successful with deposits that adhere relatively loosely to the

bags.  The vibration or rapping produces stresses at the fabric-

cake interface, causing release of the dust cake from the fabric.

Sonic Assist:  Engineers have attempted to produce agitation

frequencies still higher than those used in vibration or rapping

with ultrasonic and sonic cleaning methods.  Although cleaning at

these frequencies slightly improves the preagglomeration of a few

fine dusts, the systems generally have not been very effective in

fabric cleaning.

3.4.2  Fabric Filter Startup and Shutdown Procedures

Preoperation Checks—

     The following checks are recommended prior to startup:

     0    Test control air lines (hydrostatically).

     0    Check air dryers that supply control air to the bag
          filters.

     0    Check dust removal system.

     0    Inspect collapse air fans for alignment and rotation.

     0    Check seals at gas inlet, collapse air, and gas outlet
          damper.

     0    Check baghouse compartments, remove debris.

     0    Check filter bags for proper installation and tension.

     0    Check and sweep thimble floors clean.  Dust buildup on
          floor during operation is positive indication of a
          broken bag.

     0    Calibrate pressure drop recorders and transmitters.

     0    Check pressure taps for leakage.
                              3-43

-------
Startup—




     Although operation of a fabric filter system is virtually




completely automatic, startup and shutdown are extremely criti-




cal.




     When the new equipment is started for the first time,  the




fan should be checked for correct direction of rotation and




speed.  The ducting, collector housing,  etc.,  should be checked




fcr leaks.  Gas flows and pressures should be  checked against the




design specifications.  Instruments should then be checked  for




correct reading and calibration adjustments made as necessary.




Control mechanisms, and especially all fail-safe devices,  should




be checked fcr cperability.




     At the first startup of the system, and also whenever  new




bags have been installed by the maintenance crew, the bags  should




be checked after a few hours of operation for  tension,  leaks, and




expected pressure differential.  Initial temperature changes cr




the cleaning cycle can pull loose or burst a bag.  It is wise to




record at least, the basic instrument readings  during this  initial




startup with new bags for ready reference and  comparison during




later startups.




     During any startup, transients in the dust generating  pro-




cess and surges to the filter house are  probable and ought  to be




anticipated.  Unexpected temperature, pressure, or moisture may




badly damage a new installation.  In particular, running almost




any indoor air or combustion gases into  a cold filter can cause




condensation on the walls and cloth, leading to blinding and*
                              3-44

-------
corrosion.  Condensation in the filterhouse may void the manufac-

turer's guarantee.  It can be prevented by preheating the filter

or the gas.

     A typical sequenced startup procedure for a large continu-

ous, automatic, multicompartment fabric filter using either

reverse air, shake, or combination cleaning is summarized as

follows:

     1.   Check to see that all system monitoring instruments are
          reading zero; especially fan motor ammeters and com-
          partment pressure manometers.

     2.   Close all system dampers except tempering air damper
           (if used).   This includes main compartment isolation
          dampers, reverse air dampers (if used), and fan modula-
          tion dampers.

     3.   Start material handling system including any motorized
          airlock devices and screw conveyors.  Hoppers should be
          empty on startup.

     4.   Sequentially start main fans, allowing each to come to
          speed before starting next fan.

     5.   Start separate reverse air fan if used and allow to
          come to speed.

     6.   Engage fan  modulating damper circuit(s).

     7.   Engage tempering air damper circuit (if used).

     8.   Slowly open main-compartment isolation dampers.  If
          dampers are opened too quickly, bags will pop open, ul-
          timately resulting in failure.

     9.   Engage compartment cleaning recircuit.

    10.   Check normalcy of readings on system monitoring instru-
          ments, especially fan motor ammeters and compartment
          pressure manometers.
                               3-45

-------
Shutdown—

     1.   After process has been stepped and is no longer e-
          volving emissions, allow baghouse to track through one
          complete cleaning cycle; this will purge system of
          process gas and collected dust.

     2.   Stop main fans.

     3.   Stop separate reverse air fan, if used.

     4.   Allow material removal system to operate for 1 hour or
          until system is purged of collected material.

3.4.3  Inspection a_nd Maint e n_aji_c_e__pu_r_i n g_ No r m a_l Ope ration

     This section presents general maintenance procedures that

car. be applied to fabric filters, on kraft pulp mill power boil-

ers and crushed stone operations.  Table 3-7 presents a checklist

cf iters that, require regular inspection.

     Plant personnel must learn to recognize the symptoms that

indicate potential problems in the fabric filter, determine the

cause of the problem and remedy it, either by in-plant action

or by contact with the manufacturer or other outside resource.

     High pressure drop across the system is a sym.pton for which

there could be many causes, e.g., difficulties with the bag

cleaning mechanism, low compressed-air pressure, weak shaking

action, loose bag-tension, or excessive reentrainment cf dust.

Many other factors can cause excessive pressure drop, and several

options are usually available for corrective action appropriate

to each cause.  Thus the ability to locate and correct malfunc-

tioning baghouse components is important and requires a thorough

understanding of the system.  A detailed list of troubleshooting

and corrective measures is given in Appendix B-4.
                               3-46

-------
  Table 3-7.  CHECKLIST FOR ROUTINE INSPECTION OF BAGHOUSE'
   Component'
          Check for:
Shaker mechanism(s)
Bags
Magnehelic gauge or
 manometer

Dust removal system
Baghouse structure
  (housing, hopper)
Ductwork
Solenoids, pulsing valves
  (RP)

Compressed air system
  (RP, PP)
Fans
Damper valves (S, PP, RF)
Doors
Baffle plate
Proper operation without
binding; loose or worn bearings,
mountings, drive components;
proper lubrication

Worn, abraded, damaged bags;
condensation on bags; improper
bag tension  (S) (RF); loose,
damaged, or improper bag
connections

Steadiness of pressure drop
(should be read daily)

Worn bearings, loose mountings,
deformed parts, worn or loose
drive mechanism, proper lubri-
cation

Loose bolts, cracks  in welds;
cracked, chipped, or worn
paint; corrosion

Corrosion, holes, external
damage, loose bolts, cracked
welds, dust buildup

Proper operation (audible com-
pressed air blast)

See above; proper lubrication
of compressor; leaks in headers,
piping

Proper mounting, proper lubri-
cation of compressor; leaks in
headers, piping

Proper operation and synchroni-
zation; leaking cylinders, bad
air connections, proper lubri-
cation, damaged seals

Worn, loose, damaged, or
missing seals; proper tight
closing

Abrasion, excessive wear
  RP-reverse pulse; PP-plenum pulse; S-shaker; RF-reverse flow.
                             3-47

-------
     Table 3-8 presents the frequency of  failure  of  basic  fabric



filter parts, frequency of inspection and inspection time,  and



time required for repairs.




     Following is a discussion of major  fabric  filter components



requiring routine maintenance:



Inlet Dusting—



     Common problems such as abrasion, corrosion,  sticking  or



plugging of dust, and settling must be dealt  with  on a routine



basis.  Abrasion can be reduced by using  special  materials  at



bends in ducting.  Corrosion can be minimized by  supplying  insu-



lation,  especially in the long duct runs, which are  most sus-



ceptible to moisture condensation.  Regular inspection will help



control  plugging and dust settling in ducts.



Blast Gate and Flow Control—



     Problems with flow control equipment are reported frequent-



ly.    The blast gate valve is especially vulnerable and should



be checked periodically and adjusted. Filter compartment  inlet



dampers  are a high-maintenance item, and  spare  parts should be



stocked.    A bad camper seal can shorten the life of bags  in  a



shake-type system, and caking bags, if not replaced, can foul



valves on the clean side of the baghouse  and  cause them to  mal-




function.  The most popular dampers for  compartment  isolation  are



air cylinder-operated poppets acting vertically (see Figure



3-7).  Maintenance on these dampers consists  of periodic in-



spection and replacement cf packing and  solenoids.  Damper fail-



ures can sometimes be detected by observation of  a differential
                              3-48

-------
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                                                     3-49

-------
pressure chart.  As the dampers open and close,  the differential



pressure swings.  If a damper fails, the absence of this pressure



swing leaves a "cap" on the differential pressure chart.  If a



high differential pressure is signaled,  the darr.pers are routinely



checked for proper operation.  If not,  the operator nust observe



damper operation through the complete cycle directly at the



baghouse.



Fans--



     Fans and blowers are reported to present many problems,



particularly those located on the dirty  side of  the baghouse



where material can accumulate on the vanes and upset the bal-

     • ^

ance.""  Ccrrcsion and abrasion of fans  can also cause problems.



The use cf pressure-style baghouses has  been dramatically re-



duced,  however, because of the necessity for on-line maintenance



and the dar.ger associated with working  on a pressure type inside



bag collector.



     Condensation and corrosion in the  fan may be alleviated with


                        10
duct and fan insulation.    Most fan housings can be drained, and



the drains should be checked regularly.



     Air flew and fan speed should be measured periodically and



belt condition and tension determined;  the fan should also be



checked fcr direction of rotation.  These checks can be combined



with routine lubrication procedures.



Entrance Baffles—



     Any baffles added to improve the distribution of gas to each



compartment and bag should be adjustable.  Baffles may  cause
                               3-50

-------
                           WAFER

                            .SEAT
                         PUSH ROD
                         AIR CYLINDER
                            OPERATOR
Figure  3-7.  Poppet valve.
               3-51

-------
problems by accumulating dust or abrading too rapidly.




Hoppers--




     Hoppers are a common problem in any fabric filter  system.




Dust flow can be facilitated by the use of vibrators and/or




heaters (if they work properly); by lining the hoppers  with




antifriction materials; by the use of air-pulsed rubber-lined




hoppers; by placing poke holes in the side of the hoppers;  or by




insulation if condensation is a problem.




     Trough-type hoppers with integral screw conveyors  are  the




most comrcr. material handling systems for kraft pulp rill power




boilers and crushed stone operations.  Dust storage in  baghouse




hoppers is a common industry practice, although this frequently




results in dust bridging and subsequent use of sledgehammers




to break the dust bridge in hoppers.  Hopper vibrators  can  be




used but are expensive and have a tendency to pack the  dust and




aggravate the problem if vibration amplitude and frequency  are




not correctly selected.




     Regular inspection of the hopper (once per shift)  is manda-




tory to alleviate problems with the suction-removal system  or




those caused by bridging of dust before they become serious.




     The screw conveyor flighting inside the hoppers is supported




every 10 to 15 feet by nonlubricated sleeve-type hanger bearings




(see Figure 3-8).  Wear on these sleeves and on outboard packed




bearings is the major screw conveyor maintenance problem.  The




most common sleeve material is cast iron, although Babbitt, wood,




and various other material have been used.






                               3-52

-------
SCREW  CONVEYOR
   FLIGHTING
                                                    BAGHOUSE
                                                     HOPPER
                                                     SIDE WALL
                                                  BOLTED FLANGE
                                                 "U" - TROUGH
FLANGED  DISCHARGE SPOUT TO
 GATHER  UP SCREW CONVEYOR
   OR AIR LOCK DEVICE
 Figure  3-8.   Typical trough hopper  and screw
               conveyor arrangement.
                          3-53

-------
Bag Replacement—




     The nost expensive maintenance operation for fabric filter




systems is the complete change of a set of bags.   This is accom-




plished by a crew of two to six men, who enter the baghouse and




disconnect each bag at the cell plate and top suspension level




and install a new bag in its place.  Two bag attachment tech-




niques are illustrated in Figure 3-9.  The purchase price of




replacement bags is given in Table 3-9.  The bag  life reported by




respondents to the questionnaire survey is given  in Table 3-10.




Tension-




     The amount of bag tension required for best  overall per-




formance varies according to the make of the equipment.  Correct




tension is a function of filter dimensions and cleaning mecha-




nism.   A bag that is too slack can fold over at the lower cuff,




bridge across, and wear rapidly.    Too much tension can damage




the cloth and the fastenings.   Shake cleaning in  particular seems




to require a unique combination of tension, shake frequency, and




tag properties for best results.    In any event, the manufac-




turer's recc-.~er.jat ions should be followed and the tension




checked periodically, especially a few hours after installing a




new bas.
                              3-54

-------
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          3-55

-------
         Table 3-9.  APPROXIMATE COST OF REPLACEMENT BAGS'
Material
Fiberglass
Nomex
Kermel
Cortex
Teflon0
Acrylic
Cost factor
1.0
2.5
= 6
= 5
= 7
1.2
c _
  Based on data from the  Mcllvaine  Fabric  Filter  Manual.
                                                                -i
  As corpared to coated fiberglass,  which  costs  0.65-1.00  per  ft"",
  depending on manufacturer  and  size of  installation.
  Reflects recent reduction  in price.
           Table 3-10.   BAG LIFE IN KRAFT PULP MILL AND
                    CRUSHED STONE APPLICATIONS
Application
Kraft pulp rill power boilers
Crushed stone industries
Bag life, months
Range
9-48
Average
15
18
Spare Stock—
     It is advisable to stock a complete set of filter elements
in case of an erergency.   The spare filter elements should be
clearly labeled and kept well-separated from used filter ele-
ments.     Table 3-11 presents a typical list of items that should
be stocked, the approximate quantities, and the approximate
delivery time and costs of parts that must be purchased.
Inspection Frequency--
     External maintenance inspection of the filter house is
usually performed daily; the filter elements are typically in-
                          10
                              3-56
spected weekly or monthly.

-------
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                                     3-57

-------
Shake Cleaning—




     Shaker mechanisms are generally simply supported from each




end by knife-edge bearings set in grooved blocks.   A fractional




horsepower motor is used with a yoke linkage to oscillate the




shaker bars (see Figure 3-10).  Shaker mechanism maintenance is




centered on the drive arrangement.  Periodic lubrication of bear-




ings and checking of alignment are required*  The  shaking




machinery should also be checked periodically for  wear.   If the




bags are not being cleaned properly, sometimes a minor adjustment




cf the shake amplitude or frequency can markedly improve cleaning,




If a safe amount of shaking still does not properly clean the




clots, it may be necessary to reduce the filtration velocity for




a few hours.




Reverse-Flow Cleaning—




     With this type of cleaning, the only maintenance requirement




is to check the rate of flow  (back pressure) and the timing




periodically to keep the residual drag at an economical  level.




Shake and Reverse-Flow Clear, in g--




     As in sha'-.e cleaning, wherever the bag is flexed the rate cf




wear is apt to be high.  Maintenance procedures outlined fcr the




shake and reverse-flow methods also apply here.




Pulse Jet Cleaning-




     Since the pulse type apparatus contains almost no moving




parts, hardware maintenance is reduced in comparison with re-




quirements for other cleaning methods.  Excessive use of air




cleaning pressure can damage bags by overstretching them.  Cor-
                               3-58

-------
               ROCKING MOTION
                                   SHAKER BAR
                                        TENSION NUTS
                                             BAG  CAP
                                               CLAMP
Figure  3-10.   Typical  shaker arrangement,
                       3-59

-------
rective measures include reducing the frequency of cleaning,

using another type of bag fabric, or reducing the abrasiveness of

the dust.

Instrumentation--

     Proper operation of fail-safe mechanisms and automatic con-

trol instrumentation is very important to the safety of the

filter cloth.    The location of all sensing instruments should

be checked to see that temperature, air flow, and other operating

conditions are being measured properly.  All instruments should

be calibrated after installation and rechecked monthly for sensor

location, leaks  (manometer), sticking, and legibility of read-
    1 n
out."1"   Instrument readings covering one complete operating cycle

should be recorded for future use in routine checks and trouble-

shooting.  This record should be posted beside each instrument.

3.4.4  Fa_bric-Filter__pp_e_ra_t_ion and Maintenance Problems Speci f ic
       to i-'r a f t _PVl p_ M: l'l ~a"nd 'Cr -_=h'ed' "S-cne' OpVrVt'i'c'n's"         "

Kraft Pulp Mill Power Boilers--

     With only two U.S. pulp mills using fabric filters to con-

trol their bark-fired power boiler emissions, information on

maintenance problems and practices is very limited.  Just one  of

tr.e two companies was able to produce some maintenance data.

     The primary problem, with operation and maintenance of the

two collectors at Simpson Timber centers on the collection hop-

pers.  They have experienced plugging problems due to the very

light nature of the collected dust.  Even though  the screw con-

veyor can adequately handle the  volume of material emptying  from

the hoppers, the material tends  to briJge.  Much  of the dust


                              3-60

-------
consists of submicron NaCl particles.  To remedy the situation,



Simpson Timber is trying out a hopper vibrator system that actu-



ates at the end of each cleaning cycle.  This system appears to



be relieving the plugging.  The Simpson personnel also hope to



develop a good method of sensing that will indicate when the



hoppers begin to plug up.  To date they have not devised a relia-



ble mechanism.



     Simpson installed a bypass chute on the baghouse hopper for



use during cleanout operations.  The screw conveyors could not



handle the large volume of material released when a plugged



hopper was dislodged, so the chute was provided to relieve the



extra load.



     Except for some operational problems that arose during the



initial few months of operation, the two baghouses have run



satisfactorily for over 2 years.  Routine maintenance is, of



course, performed.  Every 3 to 6 months, when the system is off



line, the fan housings and impellers are cleaned by blowing them



out with compressed air.  Vibration detectors have been installed



on the fan to warn of impending imbalances.  This system allows



maintenance personnel to clean the fans before a scheduled in-



spection if needed.



     Bag life is reported to average around 15 months.   The usual



cause of bag failure is abrasion against the support cage.



Crushed Stone Processes—



     Since the baghouse systems serving crushed-stone processing



plants are small and many have been installed within the past 2
                              3-61

-------
or 3 years, maintenance data are very sketchy.   Plant personnel




rarely keep adequate records.   The major problems seem to be




related to the cleaning mechanism and the dust-removal system.




Minor problems occur with other segments of baghouses, but




generally operating experience with fabric filtration in the in-




dustry has been good.  Downtime for maintenance usually is not  a




serious problem because many of the processing  operations do not




run continuously.   Baghouse maintenance can be  done during non-




operating periods unless extensive repairs are  needed.




     Even though pulse-jet cleaning mechanisms  have few moving




parts when compared with shaker-type systems,  they may cause




their share of operating difficulties.   At one  plant, visited




during this study, major maintenance items were the blow-down




valves and diaphragms associated with the pulse-jet system.




These components failed at the rate of almost  one a week.  Prob-




lems were also encountered with the air compressor bearings and




drive belts.  The bearings had to be replaced  after only about  4




months of use, and the drive belts also wore quickly.  In addi-



tion, the pulse-jet system was regulated by solid-state circuit




cards, which have sometimes failed and needed  replacement.




     Another plant, reported similar difficulties with their




pulse-jet system.  Diaphragms have failed, and the cycling mech-




anism has malfunctioned on several occasions.




     Problems with dust removal/conveying systems have plagued




several of the baghouse installations surveyed.  Failure of




rotary air locks to remove collected dust from hoppers fast
                               3-62

-------
enough is a common complaint.  This sometimes results in the




material packing in the hopper as it backs up, bridging the



opening just above the airlock.  It then becomes necessary to rap



the outside of the hopper to dislodge the dust.  Screw conveyors



also are reported as a fairly major maintenance item.  At least



two installations reported broken shafts resulting from over-



loading the screw.  Maintenance personnel at one plant experi-



enced repeated problems with broken shaft pins.  The shaft pin



connects the motor shaft to the screw shaft and will shear when



the screw overloads while the motor still tries to turn at a



constant speed.  This problem was most pronounced upon startup on



the morning after collected dust had remained in the hopper and



screw overnight.  The baghouse is now run for a short period each



night before shutdown to clear the screw of any remaining ma-



terial.



     Other baghouse installations surveyed reported no particular



maintenance problems with their dust conveying systems other than



routine maintenance, e.g., repacking bearings, cleaning out



solidified material.  One of the maintenance personnel recom-



mended that baghouse manufacturers provide access panels beneath



the screw conveyor for easier cleanout.  With present designs,



someone must enter the baghouse hopper with a light and dig out



the screw from above.



     This employee also suggested that baghouses be equipped with



some sort of warning device, either a flashing light or rotating



flag, to indicate when the screw shaft breaks from the motor
                              3-63

-------
shaft.  From a distance, it is difficult to tell that the screw



has stopped turning because the drive motor continues to operate.



     The ID fans used with the pulse-jet type baghouse are a



relatively low maintenance item.  One plant reported  that they



check the fan impeller housing every 3 to 6 months, depending on



the ambient weather conditions.  Because dust buildup on the im-



peller blades causes an imbalance and increases bearing wear, it



is advantageous to keep the fans reasonably clean.  Erosion of



the blades is not a problem because the rock dust is  not highly




abrasive.



     Bag life in fabric filters at crushed stone plants may range



frcm 9 r-.cnt.hs to 4 years or more.  The average bag  life in the



industry appears to be about 1-1/2 to 2 years.  The usual cause



cf bag failure is abrasion against the cage supports  (for pulse-



type collectors).  Excessive moisture in the baghouse inlet air



during wet ambient conditions may pose a problem of bag caking.



In most cases, however, dry dust emissions are minimized curing



wet weather and the ccllectors can usually be turned  off.
                              3-64

-------
                     REFERENCES - SECTION 3
 1.  Bump, R.L.  Precipitator Design for LowrOdor Boilers Offer
     Special Problems.  Pulp and Paper.  October 1976.

 2.  Henderson, J.S.  Precipitator Survey on Non-Contact Recovery
     Boilers, TAPPI Volume 58, May 1975.

 3.  Bump, R.L.  Electrostatic Precipitator Maintenance Survey.
     TC-1 Committee of the Air Pollution Control Association.
     1974.

 4.  Environmental Pollution Control Pulp and Paper Industry,
     Part I; Air.   EPA-625/7-76-001, Chapter 16, p. 16-17.
     October 1976.

 5.  Cross, Frank L. and Howard E. Hesketh.  Handbook for the
     Operation and Maintenance of Air Pollution Control Equipment,
     Pages 56-57,  Chapter III.  Technomic Publishing Company,
     Westport, Connecticut.  1975.

 6.  Reference 2,  p. 48.

 7.  Stern, Arthur C.  Air Pollution.  Third Edition, Volume IV,
     Ch. 3, p. 130.  1977.

 8.  Jones H.R.  Fine Dust and Particulate Removal.  p. 164,
     Noyes Data Corporation.  Park Ridge, N.J., 1972.

9.    Industrial Air Pollution Control.   Chapter 7.  PEDCo Envi-
     ronmental, Inc., prepared for U.S. Environmental Protection
     Agency, Environmental Research Information Center EPA-625/6-
     78-004, June  1978.

10.  Billings, C.E. and J. Wilder.  Handbook of Fabric Filtration
     Technology,  Volume I.  Prepared by GCA Corporation for the
     National Air  Pollution Control Administration, Contract No.
     CPA-22-69-38, December 1970.
                              3-65

-------
                            SECTION 4

              'FRACTIONAL EFFICIENCY RELATIONSHIPS

4.1  INTRODUCTION

     This section evaluates the total mass and fractional effi-

ciency capabilities of precipitators, scrubbers, and fabric

filters on Kraft pulp mill and crushed stone industry processes.

Unfortunately, the availability of fractional efficiency test

data on these processes is very limited, and numerous contacts

with users and manufacturers have yielded none;  however, fraction-

al efficiency test data for electrostatic precipitators (ESP's)

on kraft pulp mill recovery boilers and a mobile fabric filter

test on a lime kiln were obtained from the literature.

     Results from computer models for ESP's and venturi scrubbers

are presented, which predict penetration as a function of particle

size.  An appropriate predictive model is not available for use

with fabric filters.

4.1.1  Limitation of Current Data

     Only in the past 4 or 5 years has particle size distribution

been measured and recorded with any regularity by control equip-

ment manufacturers, independent testing companies, and consultants;

and because of operator error and the inherent technical limita-

tions of some particle-sizing instruments, reliable data are still

not readily available.  Meaningful evaluation of fine particulate

emissions will require development of a reliable and consistent

fine-particle measuring technique that can be applied widely.  A
                                4-1

-------
broadly applicable technique for compliance monitoring  of  fine-

particle sources would have the added advantage of  enabling  the

collection of valuable data concerning the subject  processes in

this report under different operating conditions.

4.1.2  S_unna_ry_of_ Inl_e_t _Particle_ Si ze Distribution  Data Used for
Prec:p i ta tor
                                 Mode 1 s
     Table 4-1 suirxnarizes the inlet particle size distribution

data used in the precipitator and scrubber model predictions.

These particle size distributions are based on data  from  various

literature sources.   (See Table 4-1.).
     Table 4-1.  SUV-MARY OF INLET FAPTICLE SIZE DISTRIBUTION'
         DATA USED IN ESP AND SCR'oBbER PREDICTION MODELS
Process
Kraft Pulp Mill
Conventional recovery
boilers
Low-odor recovery boilers
Bark/fossil fuel-fired
boi ler s
c ^ u ~ ~ e n i -1 e kilns
Crushed S t c r. e Industry
Jaw crushers
Conveyers
x , um

1.4-1.9
1.5
5-15
20

200
10
cg, pm

3.0-2.04
2.5
2.5-4.0
4 5

8.7
4
Reference

1,2
3
4
5

6
6
                              4-2

-------
4.2  PROCEDURE FOR DETERMINING FRACTIONAL EFFICIENCY PERFORMANCE



4.2.1  Electrostatic Precipitator Computer Model



     Two computer models used to predict precipitator performance



were described earlier  (Section 2.3.2).  In the first model



reentrainment losses are assumed to be negligible.  Because



reentrainment does occur with precipitators installed on bark and



combination-fired boilers, another theoretical model is presented



in Section 2.3.2 to account for it.  This section presents selec-



ted results of applying the model to predict the fractional



efficiency of an electrostatic precipitator.



Model Application to Conventional and Low-odor Recovery Furnaces—



     The first theoretical model described in Section 2.3.2



(specifically equation 17) can be used to compute the outlet



particle size distribution and fractional efficiencies for given



values of inlet particle size distribution and required overall



mass collection efficiency.  Part of the program logic involves



an iterative procedure in which the parameter, K, is adjusted



until the computed efficiency is close to the desired value



within specific limits.  Once an appropriate value of K has been



determined, the fractional penetrations can be estimated by use



of equation 15.



     Figure 4-1 shows particle penetration as a function of



particle diameter for precipitators applied to conventional and



low-odor recovery furnaces.  The minimum collection efficiency



occurs in a particle size range of 0.2 to 0.6 ym.  The reason is



that the electrical mobility of particles is at a minimum in this
                              4-3

-------
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4-4

-------
size range.  Note that the field charging equation is important



for particles greater than 0.5 ym.  The equation predicts parti-



cle mobilities that increase with increasing particle size.   The



diffusion charging theory predominates with respect to collection



of particles smaller than 0.5 ym.  This theory predicts that the



particle mobility decreases with increasing particle size, and



minimum mobility occurs in the size range of 0.4 to 0.7 ym.



Thus the range of 0.2 to 0.6 ym presents the most difficult size



range for operation of electrostatic precipitators.



     Figures 4-2 and 4-3 are similar plots of penetration as a



function of particle size for selected overall mass collection



efficiency levels based on two inlet distributions having coarser



particles.  Although the range for minimum collection is still



0.2 to 0.6 ym, the absolute fractional efficiencies at the same



overall mass collection efficiency depend very strongly on the



inlet size distribution.  For example, at 0.3 ym and at an over-



all mass collection efficiency of 99.9 percent, Figure 4-1



indicates a fractional efficiency of 98.9 percent, whereas Figures



4-2 and 4-3 show fractional efficiencies of 97.8 and 97.0 percent,



respectively.



     One set of fractional efficiency test data for an ESP on a



kraft pulp mill recovery boiler was obtained from a report by



Gooch, et. al. of Southern Research Institute  (SRI).   These



results show an average overall mass collection efficiency of



99.96 percent with a minimum average collection efficiency of



99.92 in the size range of 0.15 to 1 ym.  The mass median diameter






                              4-5

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                                       •o
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-------
                                                   T)
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                                                    (0
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                                                    QJ

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4-7

-------
of the particulate entering the collector was approximately 1  urn.


Figure 4-4 presents fractional efficiency results  obtained  by


SRI using an electric aerosol analyzer and inertial  impactors.


Collection efficiencies are uniformly high between 0.1  and  10  um,


but decline slightly below 0.1 um,  contrary to what  would be


expected by theory.  The SRI model  underpredicts efficiency below


1 um, presumably due to the method  in which particulate space

                                      Q
charge is calculated within the model.   Above 1 um,  the SRI


model cverpredicts efficiencies because of reentrainment effects

                        g
en the larger particles.   Research-Cottrell's model would  show


results similar to the SRI model if applied to the same situation.


(See Figure 4-1, at 99.9 percent efficiency, for example.)


     Another set was obtained from  the Fine Particle Emission


Information System (FPEIS) for an ESP on a kraft pulp mill

                9
recovery boiler.   The results from a number of these tests are


presented in Figure 4-5.  Overall mass efficiencies  ranged  from


95.89 to 99.34 percent.  As shown in Figure 4-5, a minimum


efficiency occurs in the 0.2 to 0.4 um range as would be predicted


by theory.  Another minimum efficiency is beginning  at  about 4


„.-, the upper reported limit of the i-pactor test  data, presum-


ably due to agglomeration of smaller particles and subsequent


reentrainment from rapping.  Figure 4-6 shows approximate  frac-


tional efficiency curves for two normal ESP's and  one with  severe


reentrainment.    The minimum point in collection  efficiency for


the normal units occurs at 8-10 um, while the unit with reen-


trainment problems shows no improvement in efficiency out  to a


particle size of 100 um.  These curves do not extend far enough

                             4-8

-------
0.01

0.05
 0.1
 0.2
 0.5
  1
  2
      20
      30
      40
        .01
                                       SRI MATHEMATICAL MODEL
                                                    • E.A.A.

                                                    • IMP.
                     0.1
                               PARTICLE SIZE.pm
                                                            i:
 99.99


 99.9
 99.6
    m
 99 2
 98 5
    m
 95 3
 90 •""
    v
 80
 70
 60
10
Figure 4-4.   Measured and theoretically calculated  fractional
 efficiency of  an ESP on a Kraft Pulp Mill  recovery boiler.8
                                 4-9

-------
    FINE PARTICLE EMISSIONS INFORMATION SYSTEM

               TEST SERIES 18
              COMPOSITE  AVERAGE
              FOR SU8SERIES 1 4 2
                          15 & 16
                          22 & 23
                          37 & 38
10
 9
 8
 7
 6
 5
.0
.9
.8
.7
.6

.5

.4

.3


.2
                       T
                      KEY
                      D

                      6

                      O
                                   SUESERIES 1  & 2
                                   S'JBSERIES 15 4 16
                                   SL'BSERIES 22 & 23
                                   SUBSERIES 37 & 38
                 PARTICLE SIZE, urn
Figure  4-5.   Penetration  as a  function of  particle size
         an ESP  on a kraft pulp mill recovery boiler.
                                                      for
                     4-10

-------
   .9
   .7

   .5
o  99
   97
   95
   90
  70
          I     I
         J	I
                             I	I
1.0
                                    10
                    PARTICLE SIZE,
                                              SEVERE
                                           REENTRAINMENT
100
    Figure 4-6.  Fractional collection efficiency of
   precipitator collecting particulate from pulp mill
                     recovery boiler. ^
                          4-11

-------
below 1 ;.m to determine whether another minimum in collection

efficiency occurs in the 0.2 to 0.4 um range.   The minimum in

collection efficiency at 8 to 10 urn for the normal units could be

the result of normal reentrainment effects.

.Model Application to Bark Combination Bark/Fossil Fuel-fired
Sciiers--

     The theoretical model for design of precipitators for bark/

fossil fuel-fired boilers (incorporating a correction factor for

reer.trair.rer.t losses) is described in Section  2.3.2.   That

formulation is used here to develop penetration/particle size

correlations.

     Equation 37 shows that a numerical integration procedure is

needed to evaluate overall mass collection efficiency.  Input

parameters consist of the following:

     i)    Known inlet particle size distribution, i.e., f (d) ,

          represented by a log normal plot and the values cf x

          and c to cover the entire particle size range.

    11)    The value of the parameter  K (equation 13)  in the

          absence of reentrainment loss.  This can be determined

          by using the iterative procedure described in Section

          4.2.1.

   lii)    The percent material fraction that is reer.trained over

          the given number of mechanical sections.  In equation

          36 these variables are r and n.

     With values for the above quantities and  equation 4 one can

estimate percent penetration as a function of  particle size.
                              4-12

-------
Precipitators installed on bark-fired and combination-fired


boilers usually have four mechanical sections.


     Figure 4-7 shows estimated collection performance as a func-


tion of particle size at four different levels  of particle re-


entrainment r.  Note that the minimum collection is still in the


range of 0.2 to 0.4 ym.  As r increases, however, the first r-


term in equation 36 is predominant relative to  the second term,


which includes the particle-size-dependent parameter, w,.  As


an illustrative example, assume that r is 0.4,  i.e. 40 percent


reentrainment, and n is 4, i.e. four mechanical sections.  In

                                     4
this case the penetrations approach r , which is 2.56 percent,


irrespective of increasing particle size.  Figures 4-8 and 4-9


are similar plots with different assumed inlet  distributions.


Experimental field test data are needed to support the validity


of this formulation.


4.2.2  Wet Scrubber Computer Model


Design Equations and Assumptions—


     Venturi scrubbers are well described in the available litera-


ture.  '    The particle collection process depends mainly upon


the acceleration of the gas to provide impaction and intimate con-


tact between the particles and fine liquid drDplets generated as


a result of gas atomization.  The other factor  that influences


the effectiveness of the venturi scrubber is condensation.  If the


gas in the reduced-pressure region in the throat is fully saturated,


condensation will occur on the particles in the higher-pressure


region of the diffuser; this phenomenon, known  as heterogeneous


nucleation, helps particle growth and also causes agglomeration,

                              4-13

-------
                                3'.
                                  — i 0)
                                  
-------
                                                     i-l •-
                                                     (CrH
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                                                      04!H  &,
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                                                      O  O  II
                                                         
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                                                 •£'E
                                                 f     '
                                                 ^ rr  —
                                                 """ -f  4J
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                                                 o-  I
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                                                    X  C
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4-16

-------
which tends to enhance collection.  Detailed particle collection

mechanisms in the venturi scrubber have been investigated by many

researchers.13'14'15

     The venturi model used in this study is based on inertial

impaction.  It is assumed that the particles do not grow during

the collection process as a result of heterogeneous nucleation

and condensation effects.  The general form of the expression for

collection efficiency with particle size i can be written as:

          Ei = 1 - exp(-K(L/G)H'i)                      (Eq. 40)

where     E. = Removal efficiency, fractional

          K  = Impaction correlational parameter  (system
               parameter)

         L/G = Outlet liquid-to-gas ratio, gal/1000 acf

          y. = Inertial impaction parameter of particle size
           1   grade, i

     Available experimental data have been used to develop a

correlation for inlet throat velocity, V,  in ft/s, based on AP

(in. H.O) and outlet L/G measurements.



                    AP             1/2
     V  =   	^	                    (Eq. 41)
      c     5.23 X 10    (L/G + 105)

     Knowing the inlet throat velocity and measured outlet L/G,

one can calculate the droplet diameter from a modified form of an

equation developed by Nukiyama and Tanasawa.

                                 1.5
          n  =       + 1>41 (L/Q)
                  t

     The system parameter, K,  is determined by an iterative

procedure based on comparison of the actual measured overall mass


                              4-17

-------
collection efficiency and that calculated from summing the in-


dividual fractional efficiencies.   For a given particle size the


inertial impaction parameter is defined below:


               0.85(C) (D )  (D )2   V
where     C  = Cunningham correction coefficient


          c  = Particle specific gravity,  g/cm


          D  = Particle diameter,  um
           P
                                                4
             = Dynamic gas viscosity,  poise x 10


          D_ = Droplet diameter, ..n


                   2\                        D
and       C  = 1 f ~  1.23 + 0.41 exp(-0.44 -&)        (Eq.  44)

                    P


     The value of K is modified during the course  of  iteration to


yield a closer match between measured  and  calculated  overall mass


collection efficiencies for given  input values of  L/G and IP.


When the "optimum" value of K has  been found, it is inserted into


the above equations to generate the outlet particle size  distri-


bution and finally the fractional  penetration for  the various


particle sizes.  This is really an averaged system parameter,


since it is not a function of any  specific particle size.


Penetration as a Function of Particle  Size--


     Figure 4-10 shows penetration as  a function of particle size


for venturi scrubbers collecting sludge lime kiln  dust.  Typical


ranges of operating parameters were taken  from general literature,


and the inlet particle size distribution was derived  from data


presented by Cheremi sinof f ,  who does  not  mention  how much soda


fume (Na-0) is present.  Since these particles are generally


                              4-18

-------
   s
    100
     90
     80
     70
     60
     50

     40

     30
     20
10
 9
 B
 7
 6
 5

 4

 3
      1
    0.9
    0.8
    0.7
    0.6
    0.5

    0.4

    0.3
    0.2
                                    I  I  I 1  I 1 I
            x • 20, • • 4.5
              (INLET)
I    1   i  1 1  I 1 r
                   1  i  I  I i i I
                                           j  1,1 l
                                                                 i ill]
                        ^^ CO O1* ^^
                        o oo —
                             o
                             CM
                                             OOOOO
                             PARTICLE SIZE,
Figure 4-10.
           Predicted penetration  for venturi  scrubbers
           on  sludge liroe-kilns,  L/G =  15.
                                  4-19

-------
considerably less than 1 um and constitute up to 2  percent of a

typical unburned lime,   they can significantly raise scrubber

pressure requirements.  Pressure drops substantially above 20 in.

H20 would be required to achieve mass collection efficiencies

above 99 percent.  In this case the use of an x and c to specify

the inlet particle size distribution is sorr.ewhat deceiving be-

cause it does not adequately reflect the preponderance of fine
     Computer-predicted penetrations for venturi scrubbers on jaw

crushers and conveyors are presented in Figures 4-11  and 4-12.

     The or.ly available fractional efficiency test data for ven-

turi scrubbers on any of the subject processes cor.es  from unpub-

lished impactor test data for a venturi scrubber operating on a

salt laden bark/oil fired boiler.   Although the inlet and outlet

tests were taken on different days,  the boiler conditions were

sir.iiar for both tests, and so an  approximate fractional efficiency

curve was prepared, and is presented in Figure 4-13.   Overall mass

efficiency for these test data is  approximately 63 percent..  The

characteristic snarp increase in penetration as particle size

decreases is evident in this cruve.

     Overall mass and some fractional efficiency pilot tests on

hogged fuel boilers have been conducted with novel type electro-

static scrubbers.  The TRW charged droplet scrubber,  the Ceilcote

ionized wet scrubber, the APS electrostatic scrubber, and the

University of Washington electrostatic scrubber are the novel

type electrostatic scrubbers which have been tested.   Table 4-2

ccrpares characteristics and performance of these electrostatic
                               4-20

-------
                         PARTICLE SIZE.
Figure 4-11.
Predicted penetration for venturi scrubbers
   on jaw crushers;  L/G = 5.
                               4-21

-------
o    o
     <"s<



 PMTJCU SIZE. w*
Figure
4-12.

    on
Predicted penetration

convevors and screens
              for  venturi

               L/G =  5.
                                                 scrubbers
      4-22

-------
   100
    50
o
t-^
I—
oc
    10
                                 OVERALL MASS EFFICIENCY = 68%

                                     "x =  0.63   og = 7.14
                      J  I  I  I  I I I
      .1
.5       1.0

    PARTICLE SIZE,
10
   Figure  4-13.   Approximate  penetration as  a  function of
         particule size for  a  venturi scrubber  operating
              on  a salt-laden  bark/oil fired  boiler.
                               4-23

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-------
scrubbers with a conventional venturi scrubber operating on a



salt-laden bark/oil fired boiler at a 20 in.  H-0 pressure drop.






4.3  EFFICIENCY RELATIONSHIPS FOR FABRIC FILTERS



     It would be desirable to characterize baghouse collection



efficiency as a function of particle size for the processes dis-



cussed.  However, manufacturers seldom base baghouse guarantees



on fractional collection efficiency.  They prefer overall collec-



tion efficiency or outlet concentration guarantees based on their



past experience with the same or a similar type of process.



There is little incentive for manufacturers to relate baghouse



performance to particle size on existing systems and as a result,



this information is practically nonexistent.   Even though frac-



tional efficiency data for baghouses in the kraft pulp and



crushed stone industries are lacking, there is adequate evidence



in the literature from other industries to document the fact that



fabric filters preserve good fractional efficiency of filtration



in the submicron particle size range.  In other words, unlike



scrubbers and ESP's fabric filters preserve high collection



efficiency for the small particle size ranges without any modifi-



cation to their design or operation.



     It must be pointed out, however, that there are several



subtleties reported in the literature regarding the actual shape



of the fractional efficiency curve for a fabric filter.  There



are reports suggesting that the collection efficiency of a fabric



filter tends to drop somewhat in the submicron particle size



range particularly in the 0.2 to 0.4 pm region.  This behavior is





                              4-25

-------
also common to scrubbers and ESP's except that in their case the




drop in efficiency is more pronounced.   in one recent report,




it is postulated that mechanisms during high velocity filtration




can actually lead to decreased filtration efficiency on larger




particles.  The three mechanisms are as follows:




     1.   Straight Through Penetration^.  Immediately after clean-




          ing, many particles collect upon the exposed fibers.




          Soon, however, a continuous dust deposit forms on the




          fabric surface and particles collect upon previously




          deposited dust.  Particles not collected by the filter,




          but which pass through without stopping penetrate the




          filter by the "straight through" mechanism.




     2.   2e_eP_aJL£.:  Once a particle lands on or in the fabric, it



          need not necessarily remain at its point of initial




          impact.  As the dust deposit builds up, pressure drop




          can increase to several times its initial value.  Mean-




          while, the fabric substrate may stretch, allowing some




          -reviously collected particles to work through.  Filter



          behavior of this sort is "seepage."




     3.   ?_i_nhole_ F_lu_a:  Srall diar.eter pinholes occur at the




          s-rface cf dust deposit on woven fabrics.  Similar




          holes on a needle-punched felt may correspond to the




          places where needles penetrated the cloth during its




          manufacture.  A plug of deposited particles may dis-




          lodge from the dust deposit and pass through the fabric




          all at once as the supporting fibers move and stretch
                              4-26

-------
          beneath it, leaving behind such a pinhole.  Particles
          which pass through the filter in this way do so by a
          "pinhole plug" mechanism.
          Therefore, particles can pass through the filter by the
          "straight through" mechanism without being stopped,
          whereas previously collected particles can make their
          way through by the "seepage" and-"pinhole plug" mecha-
          nisms.  In addition, the fraction of the total fabric
          filter penetration represented by "pinhole plugs" can
          be as high as 70 percent.  This could account for the
          presence of large particles on the outlet side of
          baghouses in amounts not expected by considering clas-
          sical filtration theory.
     One set of fractional efficiency test data was obtained from
the FPEIS   for U.S. EPA's mobile fabric filter applied to a lime
kiln at a kraft pulp mill.  Results from a number of these tests
are presented in Figure 4-14.  Overall mass efficiencies were
above 99.9 percent.  Penetration in the 0.4 to 10 ym range is
less than 1 percent.  A minimum efficiency occurs at approxi-
mately 0.8 to 1.0 ym.
     None of the plants contacted during this study could provide
fractional efficiency information.  In fact, many of the crushed
stone installations did not ever have total mass efficiency data
since their control systems had never been tested for verifica-
tion of the manufacturer's efficiency claim.  Therefore, the
subsequent discussion is limited to a review of reported overall
efficiencies in the two subject industries.
                              4-27

-------
              KIT
      5.C
      0.5
  §
  *f
  S
     0.10
     0.05
     0.0'
        0.1
              D
              C
TEST SERIES 105.
UST SERIES 105.
TEST SERIES 106,
TEST SERIES 106.
SUBSERIES 5 » 6
SUSSERIES 21 1 22
SUBSERIES 13 I 14
SJBSER1ES 21 t 22
TEST SERIES 107. SuBSERIES  516
                      T
         FINE PARTICLE E*!SSi>
                                                       STSTE"
                                            AVERAGE
                   TEST SERIES 105
                    Si'SSERIES 5 I 6.  21 I 22
                   T£S* SERIES 106
                    SLBSEKIES
                   US' SERIES 107
                                                t 14. 21  I 22
                                     SuBSERIES 546
    0.5    1.0
                                        5.0    10
                                  PARTICLE DIAMETER,
                             50
IOC
Figure  4-14.  Penetration  as  a  function of particle size
for a  mobile fabric filter on a  kraft  pulp null  lime  kiln.
                              4-28

-------
4.3.1  Bark-Fired Power Boilers in the Kraft Pulp Industry



     Neither of the two pulp mills contacted had fractional



efficiency information for the baghouses servicing their bark-



fired boilers.  The overall mass efficiency, however, is reported



to range from 90 to 95 percent in one unit with outlet loadings




of 0.01 and 0.04 gr/scf adjusted to 12 percent CCu.   This lower



than normally expected efficiency for a fabric filter assumes



that a certain number of the bags are always leaking or broken.



The other facility reports an efficiency of 99.0 percent.  Because



the logs used in the former pulp mill are stored in  seawater, the



particulate emissions from the bark boilers contain  a high per-



centage of sodium chloride.  These particles are generally in the



submicron range and contribute to atmospheric haze.   The plant



personnel at this firm reported that the primary reason for



installing baghouses on both boilers was to reduce the emission



of submicron particles.  After installation of the baghouses, the



boilers have been effectively meeting the applicable opacity



regulations, suggesting that these fabric filters are efficient



collectors for submicron particles.  The reported overall effi-



ciencies of 99 percent fromthe latter non-salt facility or higher



are typical of fabric filters in general, and this same level of



efficiency could be extrapolated to other bark boilers.



4.3.2  Crushed Stone Operations



     Again, very little data are available on actual efficiencies



of baghouses servicing stone crushing operations.  There have



been no known fractional efficiency tests reported in the litera-
                              4-29

-------
ture.  The majority of emission tests report only the effective-




ness of the dust control system regarding compliance with local




emission regulations.  Table 4-3 presents the overall mass




efficiency data for baghouses installed at a crushed stone plant,




These data are taken from errission test results reported in the




1iterature.




     Table 4-4 presents data on overall collection efficiencies




c: fabric filters at plants contacted during the course of this




study.  It also includes the efficiencies of baghouses at two




crushed stone plants visisted during the study.  These are in-




dicated as Plants 5 and 6.
                               4-30

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-------
   Table 4-4.  BAGHOUSE PARTICULATE EFFICIENCIES - SURVEY DATA
Plant number
1
2
3
Dust source
NA
Five stone crushers
Ten pickup points including
crushers, impactors, belts, etc.
Overall mass
efficiency, %
99.0
99.88
99.0



               Stone dryer

               Stone crushing, screening, and
                conveying

               Fine grinding
               Secondary crushing and screening
               Storaae silos
= 100.0

   99 +
   99.0
   99.9
   99.8-99.9
NA = I.-.f crrat ion not available.

     The above data indicate that baghouses servicing stor.e-

crushir.g operations have an average overall efficiency in excess

of 99 percent by weight.  This high efficiency is in part a

result of the coarse nature of dust emtted fron stone crushing

coeraticns.
                               4-32

-------
                      REFERENCES  SECTION 4
 1.  Gooch, J.P.  et al.   Particulate Collection Efficiency Mea-
     surements of an Electrostatic Precipitator Installed on a
     Paper Mill Recovery Boiler,  Southern Research Institute.
     May 1971, PB 255-297.

 2.  Oglesby, S.  and G.B.  Nichols.  A Manual of Electrostatic
     Precipitator Technology,  Part II:  Application Area, p. 345
     (1970) PB 196-381.

 3.  Paul, John E.   Application of ESP's for Control of  Fumes
     from Low Odor Pulp Mill Recovery Boilers,  JAPCA Vol. 25,  No.
     2.  1975.

 4.  Cupp, Stanley, J.   Operating Experience with a Boiler Firing
     Salt Water Borne Hogged Fuel.  Crown Zellerbach Corp., Port
     Townsend Division,  Port Townsend, Washington, 1978.

 5.  Cheremisinoff, P.N.  and R.A. Young.  Air Pollution  Control
     and Design Handbook,  Marcel  Dekker, Inc.,  New York,  New
     York.  1977.  p. 841.

 6.  Vandegrift,  A.E. et al.  Particulate Pollutant Systems
     Study - Vol. 3:  Handbook of Emission Properties, Midwest
     Research Institute.   May 1971, PB 203-522.

 7.  Feldman, P.L.   Effects of Particle Size Distribution on the
     Performance  of Electrostatic Precipitators.  Presented at
     the 68th annual meeting of APCA, No. 74-02.3, (June 15-20,
     1975).

 8.  Gooch, J.P.  et al.   Particulate Collection Efficiency Mea-
     surements on an Electrostatic Precipitator Installed on a
     Paper Mill Recovery Boiler,  Southern Research Institute,
     EPA-600/2-76-141,  May 1976.

 9.  Riggenbach,  J.D. et al.  Fine Particle Emissions Information
     System Series Report,  Test Series No. 13,  Environmental
     Science, Inc.  1973.

10.  Nichols, Grady B.   Particulate Emission Control from Pulp
     Mill Recovery Boilers with Electrostatic Precipitators in
     IEEE Transactions on Industry Applications, Vol. 1A-13,
     No. 1, January/February 1977.


                              4-33

-------
11.   The Mcllvaine Scrubber Manual,  Vol.  I,  The Mcllvaine Co.,
     1974.

12.   Wet Scrubber Systems Study,  Vol.  I,  Scrubber Handbook,
     A.P.T.,  Inc., PB 213 016 (July  1972).

13.   Johnstone,  H.F., R.B.  Field, and  M.C.  Tassler.   Industrial
     Engineering Chemical,  Vol.  46 1601 (1954).

14.   Johnstor.e,  H.F.  and F.O. Eckman.   Industrial Engineering
     Chemical,  Vol. 43,  1358 (1951).

15.   Nukiyama,  S. and Y. Tanasawa.  Trans.  Soc. Mech.  Engrs.,
     Japan,  Vol. 5 62-68 (1939).

16.   Rydholm,  S.A.  Pulping Processes,  Inter science  Publishers,
     New York,  New York.  1965.   p.  802.

17.   The Mcllvaine Scrubber Manual,  Vol.  II, Chapter IX,  p.  32.2.

IS.   Mcllvair.e,  R.W.   Fine  Farticulate  Scrubbing New Problems and
     Solutions  in Second EPA Fine Particle  Scrubber  Symposium.
     New Orleans La., May 2-3,  1977.  EPA-600/2-77-193."  Ccrpiled
     by R.  Parker and S. Calvert.

19.   Private corj-.unication  with  Paoer  and pulp company,  Au crust
     1978.

20.   Leith,  D.  et al.  High Velocity High Efficiency Aerosol
     Filtration, EPA-600/2-76-020.  January 1976.

21.   Fine Particle Emissions Information  System Series Report,
     Test Series Nos. 105,  106,  and  107,  Selected runs;  Monsanto
     research Corp.,  EPA Contract No.  63-02-1816, 1975.
                               4-34

-------
                             SECTION 5



                   SUMMARY AND CONCLUSIONS





     This report reviews the use of conventional control devices



 (ESP's, scrubbers, and fabric filters) for limiting particulate



emissions from kraft pulp mill and crushed stone industry proc-



esses.  Principal areas of study are:  important design param-



eters, operation and maintenance procedures, and fractional



efficiency capability of each control device.  The following



sections summarize the report and present conclusions drawn from



each area of study.



5.1  DESIGN PARAMETERS



     In evaluation of alternative methods of particulate control



for each of the subject processes, it became clear that one type



of control device usually predominated.  For example, nearly all



kraft recovery boilers are controlled with ESP's.  Some scrubbers



have been installed on U.S. kraft recovery boilers, but only as



retrofit controls.  Smelt dissolving tanks are controlled by low-



energy scrubbers, and lime kilns, almost exclusively by venturi



scrubbers.  One U.S.  mill has retrofitted an ESP to serve three



existing kilns.



     Combination bark/fossil-fuel boilers are an exception, in



that ESP's, scrubbers, and fabric filters all have been used for




control of particulate emissions.  Use of these devices is
                               5-1

-------
relatively new and until recently bark/fossil-fuel boilers were




controlled with mechanical collectors.   Where hogged fuel con-




tains salt accumulated during transport by sea,  the fine salt




particles can cause excessive opacity of the plurr.e.  In these




circumstances only venturi scrubbers and fabric  filters have been




used for particulate control.  Presumably since  ESP manufacturers




will guarantee meeting transmissometer opacity but not visible




opacity regulations when salt-laden fuel is burned, no ESP's have




been installed on bark boilers with a salt emission problem.




     In the crushed stone industry, fabric filters are preferred




for control at point sources.  Wet suppression is also used alor.e




and in conjunction with fabric filters, and low-energy venturi




scrubbers have been used on conveying and crushing processes.




High-energy venturi scrubbers would provide better performance,




but none are presently in use.




     General advantages and disadvantages of applying ESP's,




scrubbers, and fabric filters to the subject processes are



presented in Tables 5-1 through 5-3.




£S?' s




     The use of ESP's on conventional and lew-odor recovery




boilers and on bark/fossi1-fuel boilers was evaluated.  Differ-




ences in ESP design for use on conventional and  low-odor boilers




are attributed to differences in temperature, bulk density,




tenacity of dust, and SO- content.  The particle size distribu-




tions in effluents of conventional and low-odor  boilers are
                               5-2

-------













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-------
                                                           g
similar, and resistivity of both process dusts is around 10  ohm-


err..


     Because of higher SO. levels,  the dust from low-odor boilers


adheres very tenaciously to the collecting plates and necessi-


tates heavy rapping.  This vigorous rapping, combined with the


lover bulk density of the low-odor boiler dust, leads to higher


re-entrain.ment of particles.   Moreover, the higher viscosity of


the low-odor boiler dust  (due to its temperature) increases the


crag force on the dust particles.  Because of these factors, the


SCA requirere.it for an ESP on a low-odor boiler is about 15


percent greater than with a conventional boiler.  Additional test


data are reeded to verify this finding.  In any event the design


SCA's for high-efficiency (99.5% or greater) ESP's on kraft pulp


mill recovery boilers should be in the range of 380 to 450 ft /


1000 acfm.

                            7    9
     The low resistivity  (10 - 10  ohm-cm) of the bark ash


causes serious problems of re-entrainment for ESF's.  A correc-


tion factor that assu-es a constant rate of re-ent ra inm.ent in each


mechanical section of the ESP is applied to the modified Deutsch


design equation fcr SCA, and accounts for this high rate of re-


er. train men t.   Thus in a high-efficiency ESP application  (99.5%


for example)  on a bark/fcssil-fuel boiler, SCA requirements would


range from, approximately 380 to 500 ft /1000 acfm assuming 40 to


50 percent re-entra inrnent of the bark ash.  Where firing of bark


would cause a salt emissions problerr, the SCA requirements would


be higher because of the smaller size of salt particles.
                               5-6

-------
Wet Scrubbers



     Emphasis in this study is on venturi scrubbers because their



particulate removal efficiencies are higher than those of im-



pingement type scrubbers, mesh demisters or packed towers.  Newer



lime kiln installations use venturi instead of impingement scrub-



bers.  Most smelt dissolving tanks use mesh demisters and/or



packed towers to collect particulate from exhaust gases.  Venturi



scrubbers are used successfully on bark/fossil-fuel boilers.



     Design requirements for venturi scrubbers for kraft pulp



mill applications (lime kilns and bark/fossil-fuel boilers)



include pressure drops in the range of 10 to 20 in. H-0 and L/G's



of 10 to 15 gal/1000 acf to achieve collection efficiencies of 90



to 95 percent.



     The effect of particle size on performance of venturi



scrubbers 'is evident in data from two recent scrubber installa-



tions on bark/oil-fired boilers, one with a salt emissions prob-



lem.  Because of the small particle size of the salt, the scrub-



ber on the boiler burning salty fuels requires a 15 to 20 in.



H-0 pressure drop to obtain outlet emissions at 0.07 to 0.18



gr/dscf depending on the salt content of the fuel.  In contrast,



the other operates at 8 to 10 in. H_0 yielding outlet emissions



of 0.02 gr/dscf.



     In crushed stone applications of wet scrubbers, since the



particles emitted from crushers are larger than those from con-



veyors, again a lower pressure drop in the crusher scrubbers will



yield higher collection efficiency.  Design requirements from
                               5-7

-------
Research Cottrell's computer model  estimates  for  crusher  appli-




cations are 5 to 16 in.  H20 pressure  drop  to  achieve  for  99.0  to




99.5 percent efficiency  at an L/G of  5  gal/1000  acf.   For con-




veyor applications these requirements increase to 8 to 21 in.  H?0




pressure drop to achieve 96 to 98 percent  efficiency  at an L/G of




5 gal/ 1000 acf.




Fabric FiIters




     Design A/C ratios for fabric filters  presently installed  on




bark/fcssil-fuel fired boilers range  from  4  to 5:1.   The  presence




cf fines in the bark mix prevents operation  at higher A/C ratio




because cf excessive pressure drops.   As an  example,  the  Simpson




Timber Co. baghouse collects ash from salt-laden  bark, with a




particle size distribution skewed largely  toward  the  submicron




range.  The average operating pressure  drop  at 10 in. HjO is 3




in. H_0 over the design  value.  The A/C ratio is  probably slight-




ly high at 4:8 to 1.  In two other  baghouses  on  bark/'fossi 1-fuel




boilers with no salt emission problem the  A/C ratios  are  4:1.   In




all three installations  the use of  pulse  jet  clearing allows for




slightly sm.aller collectors by the  increase  in A/C ratio.  Use cf




a mechanical collector preceding the  baghouse is  mandatory to




collect hot cinders that could cause  fire.




     In the crushed stcne industry  the baghouse  is likely to




remain as the preferred  control device because  the dry, inert




dust often can be used as a stone product  or recycled within the




plant.  Particles from the various  crushed stone processes are




coarse enough that A/C ratios as high as 7.5:1  are used  in con-






                               5-8

-------
junction with pulse jet cleaning.  Shaker cleaning with A/C



ratios of 2 to 3:1 is also popular.  Pressure drops from respon-



dents in this study range from 2 to 8 in. H_0; the finer parti-



cles from tertiary crushing and screening cause the higher



pressure drops.



     In both industries studied, and in most applications,



fabric filter operation is relatively insensitive to process



variables such as chemical composition, particle size, and re-



sistivity, although chemical composition of particles can cri-



tically affect fabric selection.



5.2  OPERATION AND MAINTENANCE



     The more stringent emission standards of recent years



require that a company follow a program of regular maintenance of



control devices to remain in compliance.  The high cost of par-



ticulate control equipment also justifies a high priority on



maintenance.



5.2.1  ESP's



     Maintenance of ESP's in the kraft pulp mill industry is



apparently more difficult than in utility or metallurgical



applications.  On recovery furnaces the most common operating



problems are corrosion and failure of rappers.  Other problems



result from drag bottom conveyors, plugging of the inlet dis-



tribution plate, buildup on ladder vanes, and "snowing" or inter-



mittent puffing of recovery furnace stacks.  Effluent from low-



odor boilers cause more problems than that from conventional



boilers because of the light, fluffy dust and the high SO-






                               5-9

-------
content, often causing corrosion.    In this application,  the




performance of an ESP can deteriorate  with time.




     Because ESP's are rarely used on  bark/fossil-fuel boilers,




little information is available on operation and  maintenance.




5.2.2  Scrubbers




     With regard to the venturi scrubber,  general operational




problems on kraft pulp mill and crushed stone processes parallel




those in other utility and industrial  applications.   They chiefly




involve ccrrosion, plugging,  and abrasion.




     Several operators of sludge lime  kilns report low mainten-




ance ar.d .-i.-.imal cperatcr attention with venturi  scrubbers.   How-




ever, in these installations, fresh water  should  be  used  instead




of contaminated condensate to minimize odorous emissions  from




stripping.




     On bark boilers, the performance  of a venturi scrubbers is




greatly affected by the quality of the water used.  The require-




ment for "bleed-off" of dissolved solids may beccr-2  difficult



because of increasing limits on water  discharge.




     No data are available on operation and maintenance of




venturi scrubbers on crushers and conveyors in the crushed stone




industry.




5.2.3  Fabric Filters




     According to respondents in this  study, fabric  filters




provide reliable service on crushed stone processes, although




maintenance data are sketchy.  Major problems are related to the




cleaning mechanism and dust removal system.  Failures of valves




and diaphrams, air compressor bearings and drive belts, and




                               5-10

-------
solid-state circuits associated with the pulse jet cleaning




mechanism have caused difficulties.  Bridging of hoppers and



breakage of screw conveyor shafts by overloading are the two most



common problems in dust removal and conveying systems.



     Data from Simpson Timber Co. indicate that overall operation



has been satisfactory; problems center on the collection hoppers,



where the light dust causes plugging.  The dust contains salt and



tends to bridge the hoppers.  Vibrators have been used success-



fully to relieve the plugging.  No reliable sensing system to



detect plugging has been devised.



     Data on the effects of various control device malfunctions



on performance of equipment are not available.  It can be stated



generally that without regular maintenance the performance of



these control devices will degrade rapidly, especially in the



fine particle size range.  This is an area where further study



could be directed in anticipation of particulate emission stan-



dards based on particle size as well as overall mass efficiency.



Additional studies could be directed to deterioration in perfor-



mance of control devices during extended operation, even with



optimum maintenance.



5.3  FRACTIONAL EFFICIENCY RELATIONSHIPS



5.3.1  ESP'S



     As expected, computer modeling of the fractional efficiency



of ESP's on kraft recovery furnaces and bark/fossil-fuel boilers



showed a minimum in efficiency in the particle size range of 0.2



to 0.6 ym.  This is due to the transition from field charging,






                              5-11

-------
which predominates for particles greater than 0.5  urn,  to collec-




tion by diffusion, which predominates with particles below 0.5




urn.  Absolute fractional efficiencies at the  same  overall mass




efficiency depend very strongly on the inlet  size  distribution.




     The predictions for bark boilers also account for the




effects of re-entrainment,  assuming that the  fraction  of material




remains constant at different particle sizes  and for each mechan-




ical section.  Minimum collection is still in the  0.2  to 0.4  urn




range.




     Fractional efficiency  curves based on test data for kraft




pulp mill recovery boilers  are available '  for comparison with




predicted results.  These test data confirm minimum collection




efficiency in the 0.2 to 0.4 -_m size range and show another




minimum in the 8 to 10 pm range, which could  be indicative of




re-entrainment.  Another test on an ESP with severe re-entrain-




m.er.t,  shows that collection efficiency continues  to decline,




leveling off at 70 to 100 '_m.  Re-entrainment in the larger




size fractions supports the idea that the dust (most cf which is



re-entrained due to rapping) consists of both large particles and




agglomerates cf smaller particles.




     Performance of ESP's on bark/fossil-fuel boilers with salt




emissions was not modeled.   The fractional efficiency, however,




probably would be reduced because of the fine salt particles,




with a resultant increase in opacity.  No fractional efficiency




test data were available for ESP's on bark/fossil-fuel boilers.
                               5-12

-------
5.3.2  Venturi Scrubbers


     The Research Cottrell computer model for predicting pene-


tration as a function of particle size in venturi scrubbers on


sludge lime kilns, crushers, and conveyors showed the character-


istic deterioration in performance at particle sizes below about

                                             4
2 micrometers.  Cheremisinoff's particle data  on sludge lime


kilns do not mention the presence of soda fume, which would add


fine particles to the mix and could lead to pressure drops higher


than those presented in the model for efficiencies above 99


percent.


     No fractional efficiency test data for venturi scrubbers on


the subject processes could be located for comparison with the


predicted performance models.


5.3.3  Fabric Filters


     A prediction model was not available for use in evaluating


fractional efficiency performance of fabric filters.  One set of


fractional efficiency test data concerns EPA's mobile fabric


filters applied to a kraft lime kiln.   This data supports the


observation that fabric filters maintain collection efficiencies


higher than ESP's or scrubbers in the submicron particle size


range.  No fractional efficiency test data are available for


fabric filters applied to bark boilers or crushed stone pro-


cesses.


     Fabric filters operating on two bark boilers with a high


percentage of submicron particles have yielded very low opacity


readings, a further indication that the fabric filters are very


efficient collectors of fine particles.  Data from the utility


                              5-13

-------
industry also show that fabric filters  can maintain  an  efficiency



of 99 percent or greater in the submicrometer  particle  size



range.



5.4  COSTS



     Estimates of capital and annual  operating costs for  ESP's



and wet scrubbers are based on data developed  by  Research Cot-



trell; estimates for fabric filters are derived from literature



sources.  Thus the cost estimates cannot be compared on the  same



basis.  The intent was to estimate costs for the  control  device



used credc.~ir.ar.tly en each cf the subject processes.  Some gen-



eral conclusions follow.



     In the past the almost exclusive use of ESP's on kraft



recovery boilers was dictated primarily by the cost  savings  in



the recovery of soda ash.  This was balanced against the  capi-



tal and operating costs over the life of the ESP, at efficiencies


                    3 8
cf £5 to 95 percent. '    In recent years, however this  savings



has been reduced because requirements for higher  precipitatcr



efficiencies have led to higher operating costs not  cffset by



the increase in rarket value cf soda  ash.  Although  retrofitting



cf venturi scrubbers downstream of an existing precipitatcr  may



provide a more economical option, such  installations are  infre-



quent and thus were not cost-evaluated.



     The predominant use of venturi  scrubbers on  kraft  lime  kilns



and of low-energy scrubbers on smelt  dissolving tanks is  dictated



by the relatively higher capital cost of installing  ESP's to



handle small gas volumes.  A recent comparison of ESP's and



venturi scrubbers on a kraft lime kiln   noted that  the  capital



                               5-14

-------
investment for an ESP is 3 times greater and that the heat loss



associated with the ESP is too great to overlook.  The venturi



scrubber was selected for the lime kiln.



     For application to bark/fossil-fuel boilers, fabric filters



are the most expensive control option, followed by ESP's and wet



scrubbers.  This observation is based on a recent report by



Weyerhauser Corp.,   which estimates the costs of installing all



three devices on a bark/fossil-fuel boiler with salt emissions.



     Comparison of fabric filter and venturi scrubber applica-



tions on crushed stone processes shows that capital installed



costs for venturi scrubbers are slightly higher and that opera-



tion and maintenance costs would be approximately 1-1/2 times



those for fabric filters.



     West dust suppresion can be used on primary crushers,



screens, transfer points, and crusher feeds, where particle sizes



are larger and moisture content is higher, in combination with



fabric filters at points where fine particle emissions occur,



primarily secondary and tertiary crushers and screens.  This



results in greater emission reduction than complete wet dust



suppression,  and is more economical than a complete fabric



filter system.
                               5-15

-------
                    REFERENCES - SECTION 5.0


1.    Figger.bach,  J.D.  et al.   Fine Particle Emissions Information
     System Series Report,  Test Series No.  13,  Environmental
     Science Inc., 1973.

2.    Gooch, J.P.  et al.   Farticulate Collection Efficiency Mea-
     surements on an Electrostatic Precipitator Installed on a
     Paper Mill Recovery Boiler.  Southern  Research Institute,
     EPA 600/2-76-141, May  1976.

3.    Nichols, Grady B.  Particulate Emission Control From Pulp
     Mill recovery Boilers  With Electrostatic Frecipitators , in
     IZEE Transactions on Industry Applications, Vol. 1A-13, No.
     1, January/February 1977.

4.    Cheremi sir.off, P.N., and R. A. Young,  Air  Pollution Control
     and Des_i_g_n Handbook. 1977, page 841.   '           '

5.    Fine Particle Emissions  Information Systems Series Report,
     Test Series Nos.  105,  106, and 107, selected runs, Monsanto
     Research Corp., EPA Contract No.  68-02-1816, 1975.

6.    Lee, David R.  An Econo-ic Comparison  of Kiln Particulate
     Control Alternatives:   Electrostatic  Precipitators vs.
     Venturi Scrubbers,  Long view Fibre Company, presented at
     Proceedings of the  1976  NCASI West Coast Regional Meeting.
     NCASI Special Repcrt No. 77-04, June  1977.

7.    See, R.C. North Bend Hog Fuel Boiler  Emission Collection
     Options.  Weyerha-ser  Co., April  1978.

8.    Rust, J.P.  Application  of Electrostatic Precipitators for
     the Control of Fumes From Low Odor Pulp Mill Recovery
     Boilers.  J. Air Pollution Control Associawtion 25 ( 2) : 158-162 ,
     February 1975.
                              5-16

-------
                    APPENDIX A-l




INSTALLATION LISTS FOR PARTICULATE  CONTROL DEVICES ON




            KRAFT PULP MILL APPLICATIONS
                         A-l

-------
                           Table A.1-1.

                             SELECTED
                    F-ESEARCH-COTTRZLL,  INC.
                 PULP KILL  RECOVERY  PRECIPITATORS
              A.  HORIZONTAL FLOW WET  BOTTOM TYPE
                      No., Type  &  Size       No.  of       Total Gas
                       Recovery  Units        Pptrs.       Flow (CFM)
                       Lbs.  BLS.a/Day &      Shell         Gas Ter.o.
     Installation     Pulp Equivalent       Material          (WF)
Y-5S13S1-C1
64C T/Day
 lor.solidated Pontiac,
Tahsis Ccr,pa_-w, Ltd.                           1            360,000
Geld River, British      3,150,000          Hollow Tile       325
Col-r-cia, Canada        1350  T/Day

International Pacer
 Oo.            "                              1
Moss Point               1,900,000           Steel
Alabama Kraft Co.                              12
Fncenix City             2,750,000           Filled
Alacar.a    "             915  T/Day            Tile

Soott-y.aritine Paper                                       191,000
Co.                      1,725,000              1             30C
Abercr-r±ie              575  T/Day           rilled
Nova Scotia                                  Tile
Canada
MarMillan  & Blcecel                            1           255, C
Lir.it e=                  2,250,OOO           Filled           325
Powell River, Br.        750  T/Day            Tile
C~l_~::ia,  Canada
                         1,650,COO           Filled           3::
~uecec, Canada           550  T/Day            Tile

Owens-Illinois  Corp.                           2           360,000
Orange               (2)  x  1,650,000  ea.     Filled           300
Texas                (2)  x  550  T/Day  ea.      Tile

In t e r = ; n 11 n en t a 1
 Pulp Co., Ltd                                 1           315,000
?r-noe George,  B.C.      2,550,000            Steel           3CC
Canda                    850  T/Dav
aBLS =  Black  Liquor Solids
(continued)


                              A-2

-------
                   Table A. 1-1  (continued).
   Installation

Tennessee River
Pulp & Paper Co.
Counce, Tenn.

Consolidated Papers
 Inc.
Wisconsin Rapids
Wisconsin

Eastex, Inc.
Evadale, Texas
Chesapeake Corp.
 of Virginia
West Point, VA

Skookumchuk Pulp
Cranbrook, B.C.
Potlach Forests
Lewiston, Idaho
Continental Can
 Co.
Hopewell, Va.

Kimberly Clark
Mexico
U.S. Plywood
Champion Papers
Courtland, Ala.

W. Va. Pulp &
Paper Co.
Wickliffe, Kentucky
No. , Type & Size
Recovery Units
Lbs. BLS.a/Day &
Pulp Equivalent
1,250,000
415 T/Day
1,200,000
400 T/Day
No. of
Pptrs.
Shell
Material
1
Filled
Tile
1
Filled
Tile
Total Gas
Flow (CFM)
Gas Temp.
173,000
325
175,000
300
                        1,600,000
                        530  T/Day
                      2,400,000  bis/
                       day
                      2,100,000
                      700  T/Day
                      900,000
                      300  T/Day
                      1,050,000
                      350  T/Day
                      360,000
                      120  T/Day
  Hollow
   Tile

2 Pilaster
 Filled Tile
    1
   Tile
  Shell

    1
  Hollow
   Tile

    1
   Steel
 Cstainless)

    1
   Steel
  Pilaster
                                           Tile Shell
                                            Pilaster
                                           Filled  Tile
                                            Pilaster
                                                        190,000
                                                        245,000
                                                          325
                                                        248,000
                                                          300
                                                        104,500
                                                          325
                                                        175,000
                                                          250
                                                         46,600
                                                          325
                                                        250, OOO/
                                                        pptr.
                                                        270,000
 BLS  =  Black Liquor Solids
(continued)
                             A-3

-------
                    Table A.1-1 (continued).
 	Installation

Boise Cascade
De Ridder, La.
Southland Paper
Mills, Inc.
Lufkin, Texas

St. Mary's Kraft
Division
C-ilr.ar. Paper Co.
St. Marys, Ga.
No., Type & Size
  Recovery Units
Lbs. BLS. /Day  &
 Pule Equivalent
 NO. of
 Pptrs
 Shell
Material
                                                        Total Gas
                                                        Flow (CFM)
                                                        Gas Temp.
                                                               '
                        1          303,000
                     Filled Tile
                      Pilaster
                      Pilled
                       Tile
                    Filled Tile
                     Pilaster
                                   140,000
             170,000
              Total
rontinental Can
 Co.
Hopewe 11 /  \'n -
Paper Co.
Erie, Penna.

•^...^.-gv-wji*.^ r"1 *•* a ^  "D a ^ o T*
* . ^ _ — ^ . * a _.*.w**3.^ * 3 ^ C *
 Co.
Texarkar.a, Texas
                    Steel Heat
                      Jacket
                    Steel Shell
                    Steel Shell
                      Opzel
             21 C , 0 0 0
               23:

             3: =, o o o
              acfn
             250,000
              325
  ELS  =  Elack Liauor Solids
(continued!
                            A-4

-------
                    Table  A.1-1  (continued)
                     B.  DRAG BOTTOM TYPE
  Installation

American Can Co.
Halsey, Oregon

International
Paper Co.,  Inc.
Glens Falls
New York

Weverhaeuser Co.
 No.,  Type
Kraft Recovery
Kraft Recovery
    1
Springfield, Oregan  Kraft Mill
Unit #4
Hoerner-Waldorf
Corp.
Missoula, Montana
Boiler *3
Western Kraft Corp.
Continental Can
Hodge, Louisiana
 Salt Cake
 Salt Cake
 Collection
 (Controlled
  Odor)
   No. of
   Pptrs.
   Shell
 Material

    1
  Steel

    1
  Steel
Opzel Filled
  Tile -
 Pilaster/
 Plenums

    1
  Steel
                        1
                     Opzel
                     Steel
                                                       Total Gas
                                                       Flow  (CFM)
                                                       Gas Temp.
164,240


180,000




249,000
207,000
  400
230,000
  365
                 390,000
                 340
                             A-5

-------
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                                                A-6

-------
Table A. 1-3.  INSTALLATION LIST FOR BARK/FOSSIL FUEL BOILERS'"
Sic
26ii
26ii
2611
2611
261
261
261
26i
26i
£61
2611
2bll
26ii
2611
£611
£611
£611
8611
£61 1
£611
2611
£611
£611
£611
£611
£611
£611
£611
£6£1
£t>£l
2621
2621
£6£1
£6£1
£621
26JI
2621
2621
£621
2621
£6£1
2621
2»>2i
£621
2621
26£1
Z621
£6£|
26£1
26<>1
2621
£621
£621
2621
Sec.
10200901
I02009H2
10fO BH« lbf«,S»HM» 9bbh«
0>FUXO PFK-(i|V t 1 HYL-f IIMF IIHU 0«2'6
Kt VERn»tuSf h-PO»EW , LONGVlEn 98bS2
NEKUOS* tD«»HUS P»PtW.H«9b. « SHOUnl^a I OOOiJ
SCUM P«Pt" 2600 FtUfH»L »VL tVKll 98iMll
Kt»C(i,C(lSM(ihULlS 9Bb37
• l.»bK» LUMHtX & PULP B« lOSo !>IIK« 99035
AL»SHA Liinhtw 4 PULP «» to^>o i>jt«« 99e3b
SCUTT PPR CO-SOI HK,li, «1<*FI,BD1 C«NAL» 7*CU«»» 9«»21
SI REGIS KkAFI.801 CANALi 1ACUMA, 9Hvei
HI HATONltK t)»207 JtSUP 3lb»i
111 RATONJEh B»?07 JESUP 31b«5
REKHIKAN PULPCU BUI 1619 KIN 9990!
I1T RATUN1ER.INC UOI299 HUOIIlAM 985SO
Jtt RATONIEK. INC BUI299 HUUlllAM <*BiSO
• ErtHAiuSlR -CO BUI Id2» IVlHttt 98«(ol
MttHAtUStK -CU BU« 1228 EVtRttl 96201
*trf HAEuStK -CO BO* 1228 EVEWtTT 982WI
HiMSUOUt PULP AND PAPEM CU MANISUOUE
ChUnN 7tLLEI>BACH.bUGALUSA
MIAL> CURPURAtlUN 4l5«,OI
BUISE CASCAUE CUBP
BUISE CASCADE CuHP
INI. PAPER Cu.lOnER XOUOVILLE R.D.NATCHE7
IM. PAPER CU.LOxEH HUUDvILlt RU.NAlCHtZ
IM.PAPtfc CU,LOr.EK »iOOny(lLLt Rl) , NAtL'Mt 1
CHAHPIUN P»K>S PASADENA TEXAS Mboi
CMAMPJUN PAHEKS P«5AUENA TEXAS 77bOl
ChAMHIUN PAHEMS PASAUtNA TEXAS 77b01
US PL'fUOO-CHAMPluN PAPER COURTL»ND RD29
US PLtxUUU-CMAMP JUN PAPER CUURILANU RU29
SUUTHLKl) PPK KILLS LUFK1N HILL MuT 103
K 1MHERL r-CLARn CORP. CHUSA PINEi
n IHBEKL T-CL«*». COUP. CKUSA HINE.S
H I«BEKH-CLAHH CORP. COUSA PINE4
ST REGIS PAPER CO 659 EASTPORT Rl) JAI FL
ST REGIS PACE" CO 659 EASTPURT RD JAX FL
CONIAINtR CORP UF AM P U HOI 709 HKENIUN
CUMAINtR CURP UF AM P U PUI 709 MHFMON
INTL PfR-ANipRnscoGi.iN MILL-JAT 01^39
IMLRt.AT 1UNAL PAPER CU TEXARKANA ItKS
bUHATERS PAPER CO CALHUUN 37309
TENH R PULP PAPER CU BX 33 tuuNCE 36326
EAS1EI INC tVAUALE 11
EASItl 1NL k»AUALt TX
B-cap.
Mlb/hr
S7o.
2£b.
0.
£99.
b9c!.
23^>.
3«0.
27u.
t>9u.
27b.
60.
IHe?.
IhS.
Ihi.
168.
«i.
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60.
90.
l««.
ISO.
33t>.
0.
1*7.
• V.
«0.
• 0.
90.
31 7.
«22.
304.
30tt.
1<6.
us.
123.
118.
193.
193.
£79.
351.
lt>0.
;BI.
«.
3a«.
Type of control
MEtnAMCAL CiiLLEClUR
MECHANICAL CULLtLttIR
MELMANICAL CULLELTliH
MECHANICAL COLLELTUR
MELHANILAL CULLEC1UR
>LCHAN|( AL CULLtLlllR
»F. F iCRUH^ER
•>E 1 SLRUHBEK
MECHANICAL CULLECTUR
MECHANICAL CULLELTUR
MSCELLANEUUS
^ELHAMIAL CuLLECTuR
MELHAMCAL tl/LLELlUR
MECHANICAL Cl'LLELtliR'1 '
•-ISCELLANEIlUS
MECHANICAL CULLELTUR
MECHANICAL CULLELlllR
MfcCHAMCAL CULLELTi.R
MECHANICAL CULLELUlK
MtLMANICAL CULLECTux
MECHANICAL COLLECTOR
MECHANICAL CULLECTUR
ME I SCRUHHE.R
MECHANICAL CULLECTUR
MECHANICAL CULLECTUR
MECHANICAL CULLELTUR
MECHANICAL COLLECTOR
MECHANICAL COLLECTOR
MECHANICAL CDLLECtUS
MtCHAMLAL LUlLlLlu1*
MECHANICAL COLLECTOR
MECHANICAL COLLECTOR
MECHANICAL COLLECTOR
MECHANICAL COLLECTOR
MECHANICAL CULLELTUR
»E 1 SCRUrihE R
*E T SLRUE>Ht-R
HE 1 SCRUMMfR
MISCELLANEOUS
ELtLIRU STATIC PREC1HI IA MlR
MECHANICAL COLLECTOR
MlSCELL»NEllU!>
Ml SLILL ANtoUb
Ml iCELLANtllOb
MECHANICAL COLLECTOR
MECHANICAL LULLEC'OR
MECHANICAL CULIECTllR
MECHANICAL COLLECTiPK
M SCELLANtoOa
»fL«AN|LAl luLLECTOR
Ml iCELLAKF.OOS
MfcMAMCAL CIICLELTOR
MMLHANllAl CIICLLLTUR
fECHAMLAL fuLLfLlUR
Eff.
bv.o
9U.O
63.0
50.0
80.0
90.11
9t'.0
96. U
9U.U
VS.O
uo.o
so. u
8b.O
Bb.O
8b.O
.0
.0
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90.0
92.0
90.0
93.0
•jb.o
•»u.o
•40.0
90. 0
65.0
/S.o
041. (1
7b."
75.0
85.0
85.0
05.0
75.0
75. u
/5.U
B«.0
99.0
99.0
7U.O
IV.V
91.0
90.0
90. U
9e!.iJ
92. U
9b.ii
95.1'
75."
9ii.O
(45. U
0-l.n
                              A-7

-------
Table A.1-3  (continued!
SlC
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<•»H
ti(\
i»t \
toil
ioc\
(KC 1
i»el
et,t \
ioe \
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t*t\
i» 1 JUt fi^t* L tJ U3 40 f*u«| >t Jul
"Ot*^t''***LUU*' •U'NU*l *4' 1 U 1
^ t J t * * L ^***t-Ow«U •IfufC'UUl' *C ^ 8 * ^ •
>tUt**t ***'*LlfOt»*!' wJ^UfL»UUU NC ^6*^6
UN|U^ C***** Cu"*1* BUi i<*fc "y^TLH'*!"' i* 1 U I
* U^ li-ftLU 3"*5««

»L.S;i«ttP»^t'»CufiK ^••^)'>

1 yh*1»{? t> i - U •-» IV 1 • v.LJr**Wtlt'"'rW r m r f m j } *J M ^ «
1 w ^ y U ^ ^ ^ Cw^S-JLlL* tu ^ * ** t * 5 *T»* * * E N i « «* ^ *t
1 w t^ U w ** u ^ C^*>3JL]C*'tL •* * P t * i win A*t N ^ * w 4 «
I^^u *4 i^ ^ • * - i / i t B .._.._ rn
I •« e W * "• v f
\ W ^ W U •• U {
• > • l U 1 J r mr i m ^ u
fci-'UlA-^ACl^lC C*' *ui !<•)»» «t.ft»G'< '•e^^b
tw^W^**W^ • — t-»WBn" t • •* WW "Wi ^! ««wi"t"*ILU a • • ' •
Iw^uvtwrf | *-t"U** C** CW «(,» il -Ul^L-lLU *>•*!*
lw?uu-»urf | fcw^ ST«lti Ki^t" Cw»t^ -Ut" »D >*»»^1
1 v £ v u ** <•> £ ! fcwL^ S'*'li P*Ptl Cu**** * 1 v t • *U J *> • u 1
lw^ww»₯^ fijc' S'**t5 ^i^tfi Co*' 3» T 3 .f
1 u t1 u u "• w f
fcw^"i^t~ WW™^ W •-•i— T pin ^ | rt™T.Oi.r<
C>,s'«|>t« CL.O- u' «•!« D •'- 41 't'S.oC"
IW^UU1*^^ •"--->JBIJ .-«r. WWf — W - - J k ' W« II3UWWI
1 W<*UU«W^
*^^OtlJ"L"J T m *- \, •• ^w-^'W VW* <>* "^t^Dt^W
ICljM ^4*t* C v**' * * ^ B*' 0*iuCit "0 *UHjLl
IC^O^^Wi t, • ^ - ~» J t ™ ' J U '» ru^r "Jl.l«''«i»"«»l^ •» 3 3 W 1
ly^yy^yj j >.l^»lCn Cu«f BullOIC Lt-lilJ'. *]1ul
lyfyyty^ Bu*C't— i CC*ULlxC LWK BulT CC'C^'w^^'y**

ly^yy^y^ Bw*Ct*s CC*uLIxC Cu*** BUiT CL^C*tC^^'y*<
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ly^yy.i | ls!k«Ml!ux«L P»*>1" iUal«T S 1 i 1 1 ux
1 y <• L J •« y it
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1 y ^ yy •* y e
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1 "EL-li nt-fN Cu t^1* kiSi»^«l «n j»i >t
1" «k b 1 i' f if-t • LU »^^ k'Sl*1-"' "U J»l *L
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ttj«ui* *•• C 1 f K . B . S^u , C «ua 3t ' 1 yfyyll
tt^-OM "«C 1 • 1 C , B . ^fy . C-L i it 11 v^uylJ
1 1 . " l. 1 i i-iCiflC.B.i^O.C-uSSt'l y^'jylj
C"-"X /tCl.£«'5*C»i CU X. j*,,'J4- n«1 Lto*X
C«V»X /tl.Lt"BALn LU X. SA-t',!* r*«T LkhAN
C«U»X ;iLLt"0«C» LU X. J1-.1J1" n«1 Lto»K
u»fxS-lLl. >t«£»P f'uD Cl» !_-»-«. I •>.-•/
t*k*> KNuC u 1 » K««-»«i 5««i/
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C"-«N /tlLt«0«C» »ti' LlXX
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• IC"«ML4L Ci'LLlCluM
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            A-8

-------
Table A.1-3  (continued)
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ludUUYud
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TKlLMANT HUl.P»P*HtK CU K•U^*U^» 5KI3U
FIBKteOtKU (.UxH MlLBUM »Vt AM1ULH
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FLAMBtAU PAPEW CU,?UO ^lKSl »Vt H, b«bbt
A»tH]CAN CAN CU t-t Nr< 1 nlj 1 Ul. ib4U4
l>•t»•lCA^ CAf, CO Pt NNJootON 3»< "36(1 lULtUU
ttUKbIA PACIFIC COMPPU BU» SBU lOLtOO
IM'L PAPt« CU LA. MILL BASlKUP LA 7l£«ri;
CUNIINENIAL CAN PUBIIUOo AUl,U!>TA 3UVU3
CuNllNEMAL CAN CU fun in t-Ul nUPEntLLBbU
• t i I t Hf, ' R>( AM CUWH I-S AT NUHth ALBANY
CHtSAPtAKt LUKPUKAIIUN UF »A »[bl PUlNl
MLNAbnA CUKfUKAIIUn JUHL/Ar. PUiNI, NOMIh
MtNAbHA CUMPUHAIIUN JUHI;AI. H01.il, NUMIH
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HuEKNtK hALUUKf CUKP 111 LAnESMOKE KUAl)
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Type of control
M.CHAMLAL LULLLLIUK
KtLMAulLAL LULLkLlt'K
MtCMANKAL CULLH.TUK
Ktl bLHUodtH
fct 1 SCXlJDUt*
^fCMANILAL CuLLtCtUK
KtLMANlLAL CULLtLlUK
HtCMAMCAL LULLtLll/N
Wl 3Ct LL AI.EuUb
KtCHANlCAL CuLLELIUH
KtCMAHlLAL LULLtLlUK
htChAKjCAL CULLtLlUt*
MlbLtLLANtUUb
fl SCtLLANtuui
htCMAMLAL CULLECIUri
HtUnAi.ILAL CULLtCluK
Kl bLELL ANt UUb
MECnAMCAL LULLtLTlJK
MtCnAlvlCAL CULLtLlUK
KtCHANlCAL CULLtLTUK
MECHANICAL CULLfClUW
MECHANICAL CULLELIUH
MliCELLA,,tUU5
M SCELLANEUUS
Mtl SCMUBBtM
MtLHANlCAL CULLtClUR
MECHANICAL CULLiCIUH
MECHANICAL CULLELlUK
MECHANICAL CULLtCluK
MECHANICAL CULLlLluK
MECHANICAL CULLtLlUK
KE 1 SLKUBBtK
RE I iCKUBBtK
MECHANICAL CULLEC1UH
MECHANICAL CULLELlUK
ELtClhu STAlJC PKtCIHMAIUK
KECnAMCAL CULLELTuM
MtLHANlLAL CULL ELI UK
MECHANICAL CULLEClUK
KECHAMCAL CULLtClUK
KELHAN1LAL CULLELlUK
MECHANICAL LULLELlUK
Ml aCtLLANt uUi
KtL'HANlLAL CULLEClUK
MlSCtLLANEUUb
MECHANICAL CULLELIUH
MECHANICAL CULLELlUK
MLhAMCAL CULLELlUK
MLHAKlCAL CULLELlUK
MtC«Ai.ILAL CULLELlUK
MECHANICAL CliLLECTtlM
KtLHAnlCAL CuLLtLltiK
MlbLELLANtDub
1-El.HANjLAL CuLLLLlux
Eff .
03. u
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            A-9

-------
                APPENDIX A-2




CAPITAL AND ANNUAL COSTS OF  PRECIPITATORS FOR




           PULP MILL  APPLICATIONS
                     A-10

-------
    5000




    4500




    4000




    3500

*•>
 o

 *  3000
 *^

 i—
 z
 LO

 £  2500
S  2000
a.
    1500
   1000
    500
                                              99.9% EFF,
                                _L
 JL
               100      200      300      400

                         GAS FLOW RATE, ACFM x 10
500
3
600
700
       Figure A.2-1.   Capital  investment for  precipitators
         on conventional (high—odor)  recovery furnaces.
                                   A-ll

-------
   1000




    900




    800




    700




Is   600

 X
«*

   - - -
t    ^
o

_i

I   400
inn
 w -
100
                                          99.95 EFF,
          100
                       200
300
400
500
600
700
                        FLOW RATE, ACFM x 10
  Figure  A.2-2.  Annual  costs for precipitators  on
     conventional  (high-odor) recovery  furnaces.
                         A-12

-------
<*•>

 o
    5000
    4500
    4000
    3500
    3000
    2500
 £  2000
 o.
    1500
    1000
     500
                                                    99.8% EFF.
    97.9% EFF.



    96% EFF.
                                                  J
               100      200      300     400


                          GAS  FLOW RATE, ACFM x TO
500

3
600
700
      Figure  A.2-3.  Capital investment for precipitators

                 on low-odor recovery furnaces.
                              A-13

-------
o
LJ
_J
«s
   1000
    900
    SDC
    60C
    43;
    3 DC
    100
                                                   99.8i EFF.
                                                   97.9%
              100
200
300
400
                         dAS  FLOW R*TE,  ACFM x 10
 500
3
600
700
       Figure A.2-4.   Annual  costs for  precipitators  on
                   low-odor recovery furnaces.
                               A-14

-------
   5000
   4500
   4000
   3500
   3000
   2500
S  2000
   1500
   1000
    500
99.9% EFF.

  99% EFF.

  98% EFF.
                                        I
              100      200      300      400

                         GAS FLOW RATE, ACFM  x 10
                                 500
                                 3
600
700
  Figure A.2-5.   Capital investment for precipitators on
      bark combination bark fossil fuel-fired boilers.
                             A-15

-------
3
   1000
    900
    soo
    700
    600
    100
             99.9i EFF.


               99i EFF.
               98i EFF.
              100
200
300
400
500
600
700
                        GAS FLOW RATE,  ACFM x 10
   Figure A.2-6.  Annual costs for  precipitators  on  bark
         corhination  bark fossil fuel-fired boilers.
                             A-16

-------
                    APPENDIX  A-3




  CAPITAL AND ANNUAL COSTS  OF VENTURI  SCRUBBERS ON




KRAFT PULP MILL AND CRUSHED STONE  INDUSTRY PROCESSES
                         A-17

-------
     Q_
     •a:
       600
        500
        400
        300
        100
          30
T »  500eF,  L/G « 10

£ *  4.2 °g  « 3.Z3
        60          90


            GAS  RATE, ACFM x 10
120
  Figure A.3-1.   Effects of collection efficiency  ana  gas
rate on the capital ir.vestrer.t of  venturi scrubber  systems
                       for lime kilns.
                             A-18

-------
       300
    o


    x
    1/5

    O

    <_>



    C5
    2
    UJ
    Q.
    O
:D
z

«£
   200
       100
           - 90% COLLECTION EFFICIENCY     /


           --- 95% COLLECTION EFFICIENCY   '


           OTHERS  INCLUDE THE COST OF    /

           WATER LABOR AND MAINTENANCE,/   T =  50o°F  L/G = 10

           ETC.                     /
                                        x =  4.2, °g =  3.23
               \x
               *v
            <$*'
            <&
                   <$>'
                 $&
                £'
&'
                                          ^~— OTHERS
          30
                  60
         90
120
                       GAS FLOW RATE, ACFM X 10
 Figure A.3-2.   Effects of  gas rate, electricity usage,

fixed charges,  and others on the annual  costs of venturi

             scrubber systems for lime kilns.
                            A-19

-------
        800
        700
  ^    600
   o


   X
   z;
   t—
   t/i
   UJ
   =»
        500
400
        300
        200
        100
          30
         Oi salt,  2% ash

         T = 390°F. L/G «  7

         x = 15, cg « 4
            60
90
120
150
180
                         GAS  FLOW RATE  (acfm x  10  )
Figure A.3-3.   Effects of collection efficiency  and cas rate

                on the capital  investment of  venturi scrubber

                systerr.s for bark/fossil fuel  boilers.
                            A-20

-------
      300
CO
 o
 IS)
 o
 o
200
      TOO
               92% COLLECTION EFFICIENCY
       	 91%  COLLECTION  EFFICIENCY

       OTHERS INCLUDES THE COST OF
       WATER, LABOR AND MAINTENANCE,
       ETC.
       0% SALT,  2% ASH
       T = 390°F, L/G = 7
       x = 15, °g = 4
                                                ED CHARGES
                        •ELECTRICITY
                    I
                                   I
         30
60         90         120        150

     GAS FLOW RATE (acfm x 10 3)
                                                     180
Figure  A.3-4.
          Effects of  gas rate, electricity  usage,
          fixed charges  and others  on the annual
          costs of venturi scrubber systems  for
          bark/fossil  fuel fired  boilers.
                         A-21

-------
o

X
     800,
     700
     600
     500
     400
     300
     200
     TOO




1.5e  salt,  high ash
T  = 400'F,  L/G « 8.5
x  » 0.38, °g « 7.1
        30
     60
90
120
150
180
                      GAS FLOW RATE (acfm x 10 J)
 Figure  A.3-5.
     Effects of collection efficiency  ar.d gas
     rate on the capital  investment  of venturi
     scrubber systems  for bark/fossil  fuel
     fired boilers.
                         A-22

-------
      300
  o

   x
  I/O
  o
  o
      200
      TOO
         56% COLLECTION EFFICIENCY
  	  52% COLLECTION EFFICIENCY

  OTHERS INCLUDES THE COSTS OF  -.
  WATER, LABOR AND MAINTENANCE
  ETC.
  1.5% SALT, HIGH ASH
  T = 400°F, L/G = 8.5
x = 0.38 °g =  7.1 &/        s
                <§S        /


                 ^
       ^Y ^
                                   FIXED CHARGES
               ELECTRICITY
         30
       60
90
120
150
180
                       GAS FLOW  RATE (acfm x 10
Figure A.3-6.
     Effects  of gas rate,  electricity usage,
     fixed charges and others on the annual
     costs of venturi scrubber systems  for
     bark/fossil fuel fired  boilers.
                        A-23

-------
    300
o
X
    200
«s
I—
o.
    IOC
          T - 75'F, L/G « 5  J - 200, °g « 8.7
       10
20
30
40
                       GAS FLOW RATE, ACFM x 10
  Figure  A.3-7.   Effects cf collection efficiency and  gas
rate on the  capital investment of  venturi scrubber systems
                     for stone crushers.
                                 A-24

-------
       CO
        o
        a.
        o
                          99% COLLECTION EFFICIENCY
                   	  99.5% COLLECTION EFFICIENCY
                          OTHERS INCLUDE THE COSTS OF WATER,
                          LABOR AND MAINTENANCE,' ETC.
           TOO
        °   80
        X
        s   6°
        o
            40
            20
                       I         I
                    75°F, L/G =  5
                    200, °g = 8.7
                  I
     FIXED CHARGES'

   i— — ***** ^*-~
              10
20
30
40
                             GAS FLOW RATE, ACFM x  10
    Figure  A.3-8.  Effects of gas rate, electricity usage,
fixed charge,  and others on the  annual costs of venturi scrubber
                   systems for stone crushers.
                                    A-25

-------
        300
        200
        TOO
              = 75°F, L/G « 5   x « 10,  cg - 4
          10
20
30
                         GAS FLOW RATE, ACFM x  10
40
Figure A.3-9.  Effects  of  collection efficiency  and  gas  rate
    on the capital  investment  of venturi scrubber  systems
                 for  stone  crushing conveyors.

-------
 ro

  O
  O
  O
  QC
  UJ
  O.
  O
                   96% COLLECTION EFFICIENCY
            	 98% COLLECTION EFFICIENCY

            OTHERS INCLUDE THE COSTS OF WATER,
            LABOR AND MAINTENANCE, ETC.
      100
       80
       60
       40
       20
                  I        I         I        I

              75°F,  L/G « 5 x = 10, °g « 4
         10
20
30
40
                       GAS FLOW  RATE, ACFM x 10
Figure  A.3-10. Effects of gas  rate, electricity usaqe,
      fixed charges^,  and others on the annual cost of
venturi scrubber  systems for stone crushing conveyors.
                                A-27

-------
                          APPENDIX B-l




            ELECTROSTATIC PRECIPITATOR SUBSYSTEM AND




                COMPONENT FUNCTION AND OPERATION






B.I.I  TRANSFORMER-RECTIFIERS




     The transformer-rectifier unit consists of a high-voltage




transformer, high-voltage silicon rectifiers, and high-frequency




choke coils.  The unit converts the low-voltage alternating




current to high-voltage unidirectional current suitable for




energizing the precipitator.




     The transformer, rectifiers, and choke coils are submerged




in a tank filled with a dielectric fluid.  The tank is equipped




with high-voltage bushings, liquid level gauge, drain valve,




ground lug, filling plug, lifting lugs, and surge arresters,




which discharge any harmful transients appearing across the dc




metering circuit to the ground.




     The electrical equipment described below comprises the




components necessary to produce and control the high-voltage




unidirectional power required to energize the electrostatic




precipitator.  The transformer-rectifier and control unit provide




a complete system for energizing with either half-wave or full-




wave voltages.  Not all precipitator installations incorporate




all of these subcircuits, but most will include many of these




features; some of the automatic features described below may be




done manually on some installations.
                               B-l

-------
     A subsystem that automatically maintains and limits optimum
     current and voltage to the high-voltage transformer, which
     is connected to the discharge wires.

     Silicon controlled rectifiers (SCR's)  that provide a wide
     range of precipitator current and voltage control.

     A current-limiting reactor that limits current surges
     during precipitator sparking.

     Automatic restart to initiate system  operation after a line
     voltage failure or temporary ground condition in the pre-
     cipitator.

     Overload protection for the high-voltage rectifiers.

     Panels containing component modules;  the SCR power circuit,

dc overload circuits, relays,  control transformers, resistors,

m.ain contactor, and current transformer and other components are

mounted in the control cabinet and are completely accessible for

servicing.  Positive ventilation for the control unit is provided

by an intake fan located near  floor level.   Ventilating air is

exhausted through an opening (grill-protected) in the upper rear

of the control unit.

     The transformer enclosure is a square  metal housing bolted

to the top of the tra-.s f crrer  tank.  The enclosure protects the

transformer bushings and electrical connections from weather and

also ensures, via a key interlock system,  that none of the elec-

trical connections or bushings can be handled until the associ-

ated control cabinet has been  de-energized  and grounded.

     The transformer pipe and  guard are used to feed the high-

voltage output of the transformer-rectifier to the support bush-

ings, which in turn are connected to the upper high-tension

support frame, from which the  discharge wires are suspended.
                              B-2

-------
Figures B.l-1 and B.l-2 illustrate vibrator rapper and insulator



assemblies and their relationship to the rest of the precipitator



system.



B.I.2  AUTOMATIC POWER CONTROLS



     During normal operation, optimization of applied power to



the precipitator is accomplished by automatic power controls,



which vary the input voltage in response to a signal generated by



the sparkover rate.  Provisions are also included to make the



circuit current-sensitive to overload and to allow control in the



event that spark level cannot be reached.  Although the circuits



may vary among installations, many of the features described



below are common.  An SCR mainline control diagram is presented



in Figure B.l-3 to illustrate operation of the automatic power



control system.



     When the circuit breaker and control circuit on/off switch



are closed, power flows through the current-limiting reactor,



current transformer, and current signal transformer to the pri-



mary of the high-voltage transformer.  The SCR's act as a vari-



able impedance and control the flow of power in the circuit.  An



SCR is a three-junction semiconductor device that is normally an



open circuit until an appropriate gate signal is applied to the



gate terminal, at which time it rapidly switches to the con-



ducting state.  Its operation is equivalent to that of a thyro-



tron.  The amount of current that flows is controlled by the



forward blocking ability of the SCR's.  This blocking ability is



controlled by the firing pulse to the gate of the SCR.  The






                               B-3

-------
DISCHARGE
ELECTRODE
 VIBRATOR
DISCHRAGE
ELECTRODE
VIBRATOR
              DISCHARGE  ELECTRODE VIBRATOR
                 AND INSULATOR ASSEMBLY
   COLLECTING
   ELECTRODE
     RAPPER

COLLECTING ELECTRODE RAPPER
  AND INSULATOR ASSEMBLY
   Figure  B.l-1.   Insulator,  vibrator-rapper assembly,  and
               precipitator  high-voltage frajne.
                            B-4

-------
   VIBRATOR
   OR RAPPER
                   BRACKET

          UPPER  RAPPER ROD
                                         POWER CABLE
                                      STUFFING BOX
                                       SEAL PLATE
     ASBESTOS PAD
     INSTALLATION
ACCESS DOOR
LOCATED TO SUIT
HIGH TENSION
DUCT CONNECTION
LOCATED TO  SUIT
                                               INSULATOR COMPARTMENT
   VENTILATING  OR  PRESSURIZING
  AIR CONNECTION-LOCATED TO SUIT

— INSULATOR SHAFT
                                               ASBESTOS PAD
                                               INSTALLATION
     LOWER RAPPER ROD
                                                SUPPORT  BUSHING
                                                  PRECIPITATOR ROOF
  Figure B.l-2.  Precipitator  insulator and  vibrator-rapper
                              assembly.
                              B-5

-------
                                   C
                                   u
                                   4J
                                   C
                                   C
                                   O

                                   O
                                   C
                                   a
                                   u
B-6

-------
current-limiting reactor reshapes the current wave form to



essentially a sine wave and limits peak current due to sparking.



     The firing circuit module provides the proper phase-con-



trolled signal to fire the SCR.  The timing of the signal is



controlled by 1) the potentiometer built into the module, 2) the



signal received by the automatic controller, and 3)  the signal



received by the spark stabilizer.           .



     The automatic control circuit performs three functions:



spark control, current-limit control, and voltage-limit control.



     Spark control is based on storing electrical pulses in a



capacitor for each spark occurring in the precipitator.  If the



voltage of the capacitor exceeds the preset reference, an error



signal will phase the mainline SCR's back to a point where the



sparking will stop.  Usually this snap-action type of control



will tend to overcorrect, resulting in a longer downtime than is



desirable.  At low sparking rates, about 50 sparks per minute,



the overcorrection is more pronounced, resulting in reduced



voltage for a longer period, with subsequent loss of dust and



reduced efficiency.



     Proportional control is also based on storing of electrical



pulses for each spark occurring in the precipitator.  The phase-



back of the mainline SCR's, however, is proportional to the



number of sparks in the precipitator.  The main advantage of



proportional control over spark control is that the precipitator



determines its own optimum spark rate, based on four factors:



temperature of the gas, dust resistivity, dust concentration, and

-------
internal condition of the precipitator.   In summary,  with pro-




portional spark rate control, the precipitator determines the




optimum operating parameters.  With conventional spark control,




the operator selects the operating parameters, which  may not be




optimal.




     Some precipitators operate at the maximum voltage or current




settings on the power supply with no sparking.  In collection of




low-resistivity dusts, where the electric field and the dust




deposit are insufficient to initiate sparking, the r.c-spark




condition ray arise.  The fact that the precipitator  is not.




sparking does net rean necessarily that the unit is underpowered.




The unit may have sufficient power to provide charging and elec-




tric fields without sparking.




     The voltage-limit control feature of the automatic control




module limits the primary voltage of the high-voltage transformer




to its rating.  A transformer across the primary supplies a




voltage control, as in the case of the current limit.  The vol-




tage control setting is adjusted for tne primary voltage rating




cf the high-vcltage transformer.  When the primary voltage ex-




oeeds this value, a signal is generated that retards  the firing




pulse of the firing module and brings the primary voltage back to




the control setting.




     For current-limit control, a transformer in the  primary




circuit of the high-voltage transformer monitors the  primary




current.  The voltage from this transformer is compared with the




setting of the current control, which is adjusted to the rating
                               B-8

-------
of the transformer-rectifier unit.  If the primary current ex-



ceeds the unit's rating, a signal is generated, as with spark



control, which retards the firing pulse of the firing circuit and



this brings the current back to the current-limit setting.



     With all three control functions properly adjusted, the



control unit will energize the precipitator at its optimum or



maximum level at all times.  This level will be determined by



conditions within the precipitator and will result in any one of



the three automatic control functions operating at its maximum,



i.e., maximum voltage, maximum primary current, or maximum spark



rate.  Once one of the three maximum conditions is reached, the



automatic control will prevent any increase in power to reach a



second maximum.  If changes within the precipitator so require,



the automatic control will switch from one maximum limit to



another.



     Other features include secondary overload circuits and an



undervoltage trip capability in the event that the voltage on the



primary of the high-voltage transformer falls below a predeter-



mined level and remains below that level for a period of time.  A



time-delay relay is also used to provide a delay period in the



annunciator circuit while the network of contacts is changing



position for circuit stabilization due to an undervoltage con-



dition.



B.I.3  VIBRATORS



     The purpose of a vibrating system is to create vibrations in



either the collecting plates or the discharge wires to dislodge
                               B-9

-------
accumulations of particles so that the plates or wires are kept

in optimum operating condition.

     The vibrator is an electromagnetic device,  the  coil  of which

is energized by alternating current.   Each time  the  coil  is

energized, the vibration set up  is transmitted to the  high-

tension wire supporting frame and/or  collecting  plates through a

rod.  The number of vibrators depends on the number  of high-

tension frames and/or collecting plates in the system.

     The control unit contains all devices for operation  of the

vibrators, including means of adjusting the intensity  of  vibra-

tion and the vibration period.  Alternating current  is supplied

to the discharge wire vibrators  through a multiple cam-tyre timer

to provide the sequencing and time cycle for energization of the

vibrators.

     For each installation, a certain intensity and  tine  period

of vibration will produce the best collecting efficiency.  In-

sufficient vibrating intensity will result in heavy  buildups of

d-ist on the discharge wires which can cause the  following adverse

operating conditions.

     It reduces the spark-over distance between  the  electrodes,
     thereby limiting the power  input to the precipitatcr.

     It tends to suppress the formation of negative  corona and
     the production of unipolar  ions  required for the  precipita-
     tion process.

     It alters the normal distribution of electrostatic forces in
     the treatment zone.  Unbalanced  electrostatic fields can
     cause the discharge wires and the high-tension  frame to
     oscillate.
                              B-10

-------
B.I.4  RAPPERS




     The rapper equipment is a completely electrically operated



system for continuously removing dust from the collecting plates



within the precipitator.  The system is composed of a number of



magnetic-impulse, gravity-impact rappers that are periodically



energized to rap the collecting plates for removal of dust de-



posits.  The main components of the system are the rappers and



the electrical controls.



     The magnetic-impulse, gravity-impact rapper is a solenoid



electromagnet consisting of a steel plunger surrounded by a



concentric coil, both enclosed in a watertight steel case.  The



control unit contains all the components (except the rapper)



needed to distribute and control the power to the rappers for



optimum precipitation.  The electrical controls provide a number




of separate adjustments so that all rappers can be assembled into



a number of different groups, each of which can be independently



adjusted from zero to maximum rapping intensity.



B.I.5  UPPER PRECIPITATOR



     On positive or negative pressure installations a pressuri-



zing fan is supplied  (located on the cold roof) to force air into



the top housing and down through the support bushings.  This air



prevents the process gases in the precipitator from entering the



top housing and contaminating the support and high-tension frame



vibrator-rapper insulators.  Electric heaters are also used to



prevent condensation buildup on the porcelain bushings, thereby



preventing electrical short circuits which may damage the bushings,






                               B-ll

-------
     In place of a top housing, some installations have insulator
compartments.  The insulator compartment is a steel enclosure
that surrounds the high-tension frame support insulators and
rapper rod insulators.  Fans are provided to prevent condensation
of noisture on the high-voltage support insulator, and sometimes
electric heaters are installed near each bushing in each insu-
lator compartment.
     The purpose of the high-tension anvil beam, which is part cf
the high-tension frame, is to transfer the impact of the high-
ter.sicn vibrator to the discharge wires.
3.1.6  DISCHARGE WIRES
     The discharge electrodes are small-diameter wires suspended
from a structural steel wire supporting frame, held taut by
individual cast iron weights at the lower end and stabilized by a
steadying frame at the top of the cast iron weights.  Unshrouded
and shrouded discharge wires are illustrated in Figures B.l-4 and
B.l-5, respectively.
~ •«  -.  ,-.^T»~«r~
-------
                                — SHROUD CAP
                                — SHROUD
                                   WIRE
                                   SHROUD
                                             Figure B.l-6.   Precipitator
                                                collecting electrodes
Figure B.l-4.  Discharge
 electrode unshrouded
 CAST
 IRON
WEIGHT
                           Figure B.l-5.
      Discharge electrode
      shrouded
                                B-13

-------
B.I.8  LOWER PRECIPITATOR




     The lower steadying frame limits or restricts the horizontal




movement of the discharge wires.
                               B-14

-------
   APPENDIX  B-2. PRECIPITATOR PREOPERATION CHECKLIST
1.)   General

     Before start-up of the precipitator(s)  and auxiliary
     equipment,  a complete check and visual  inspection of
     the following items should be performed.

2.)   Precipitator
a)    Duct spacing .

b)    Collecting plates

     0  Bowing
     e  Bellying
     0  Supports
     0  Spacer bars
     0  Corner guides

c)    Gas sneakage baffles

d)    Anti-swing devices

e)    Hoppers

     0  Dust level  indicators
     0  outlet connections
     0  Access doors
     e  Poke holes - anvils
     0  Vibrators

f)    Insulator housing
        Support bushings
        Access doors
        Ventilation system
        Bushing connections
        Bushing heaters
                              Check Initial Date Recheck Remarks
                           B-15

-------
                                      Check
Initial
Data
Fecheck
Remarks
g)   Flues

     •  Nozzle connections
     •  Expansion joints
     •  Louver dampers
     •  Guillotine dampers
     •  Perf.  distribution
        plates

h)   Line voltage

     •  460/480 vclts-60 Hz
     •  575 volts - 60 Hz
     0  120 volts
     •  Line matching transformer

i)   Discharge electrode wires

     •  Upper steadying frame
     •  Lower steadying frame
     •  Hanger pipes
     •  Lifting rods
     •  C.I. weishts -
        15   25 ' 35

j)   High-tension guard

     •  Installation
     •  Vent ports open
     •  Ground connections

k)   Drag bottom conveyor

1)   Wet bottom agitators

m)   Keat packet system

     •  Fecirculating fan
     •  Electric heater - kW
     •  Steam heater coils
     •  Temperature transmitters
     •  Pneumatic recorders
     •  Steam, control valve
     •  Starters - pushbuttons
     •  Thermostats

fi)   Roof enclosure

     •  Ventilation
     *  Air conditioning
     *  Monorail system
     •  Roof exhausters
     •  Louvers
     •  Heaters
                                     B-16

-------
o)   Gaskets for high
     temperature


3.)  Auxiliary Equipment

a)   Transformer-rectifier
     units
     e
     o
     o
     0 O
     o o
     o o
     o o
     o o
     o o
     o o
     o o
Surge arrester gap
Transformer liquid level
Ground connections
Precipitator
Transformer
Rectifier
H.T. bus duct
Conduits
FW/HW switch box
Alarm connections
Contact making
thermometer
Ground switch
operation
High-voltage connections
Telephone jacks
Sound power jacks
Resistor board
Space heaters
b)   Rectifier control units

     0  Controls grounded
     e  Connections to
        equipment
     0  Space heaters
     e  Internal light and
        switch
     e  Alarm connections
     0  Space heaters

c)   Rapper control unit
        Connections
        Lights
        Space heaters
d)   Vibrator control unit
     •  Connections
     •  Lights
     0  Space heaters
Check



































Initial



































Data



































Recheck














.




















Remar



































                            B-17

-------
e)
f)
h)

i)

3>

k)

1)

m)


n)

o)

P)

q)
F.D. Ventilation
controls

•  Motor
•  Starters
•  Pushbutton stations   j
•  Alarm connections
0  Filters

Electric heater controls

•  Hoppers
0  Insulator housing/
   cor.par trr.ent
8  Roof enclosure
8  Control house

Control house

0  Heaters
0  Ventilation
0  Motor control centers
0  Distribution
   par.elboards
'  Lighting panelboards
•  Starters

Screw conveyors

Rotary feeder valves

Zero speed detectors

Speed reducers

Trough type hoppers

Inner doors - drag bottom
level

Air vibrators-Navco 3 in.

Air vibrator controls

Water spray piping

Pillow block asserr\bly
                              Check
                                Initial
Data
Recheck
Rerr.arks
                           B-18

-------
r)   Automatic back draft
     dampers

s)   Filter boxes - filters

t)   Butterfly dampers
Check



Initial



Date



Recheck



Remarks



                          B-19

-------
                          APPENDIX B-3

             ELECTROSTATIC PRECIPITATOR INSPECTION,

           MAINTENANCE, AND TROUBLESHOOTING PROCEDURES


B.3.1  TR.nNSFOR.XER-RECTIFIER SETS AND ASSOCIATED EQUIPMENT
       AND CONTROLS

     Check the liquid level in the transforitier weekly.  If  it  is

low, fill the tank to the level indicated on the gauge with the

dielectric liquid specified on the nameplate.  Dielectric fluid

sr.ruld be handled with extreme caution.

     Clean high-tension insulators, bushings, and terminals

during each outage to minimize surface leakage.  Glazed porcelain

is rest cleaned with a damp cloth and a nonabrasive cleaner.

     Once each year or more often, clean the contacts of relays

and dress them with a fine grade of crocus cloth.

     Check the dustcp filter weekly.  The air filter assembly,

easily attached and convenient for servicing, is mounted on the

control cabinet.

     7r an_s_f c_r~_e_r_ Enc losure

     Inspect all bushings and insulators.  Replace those that  are

caraged;  clean those that are dusty with a nonabrasive cleaner.

     Clean all interlocks and lubricate with powdered graphite to

e-.sure smooth and proper action.

     Lubricate all bearing points on the ground-operator lever,

connecting rods, and bevel gears.
                                B-20

-------
     Check all electrical connections to ensure that they are



corrosion-free and tight.  Loose electrical connections can cause



electrical erosion of connections and failure of metering cir-



cuits and electrical components in both the control cabinet and



transformer.



     Pipe and Guard



     Remove all internal rust and/or scaling.  Rust appearing on



the internal walls of the guard could peel off and fall against



the pipe, causing a ground on the secondary of the transformer.



     Check the condition of the wall and post insulators for



signs of electrical tracking (arcing), dust buildup, and cracked



insulators.  Clean or replace parts as required.



     Check the pipe to ensure that all connections to wall



bushings and post insulators are tight and that the pipe elbows



used to redirect the pipe at various turns in the guard are tight



and secure.



     Ensure against water leakage by checking and maintaining the



seal on the inspection plates of the pipe and guard.



     When replacing the inspection covers, be certain to rein-



stall the ground jumper between the guard and cover plate; this



ensures that any static charge or high-voltage leak goes to



ground.



B.3.2  VIBRATORS



     Inspect each vibrator for proper gas setting.



     Inspect boot seal for holes or tears and replace if nec-




essary.
                             B-21

-------
     Inspect the service sheet gasket between the guide plate and




the mounting nipple for signs of deterioration and replace if



necessary.




     If boot seal or service sheet casket has deteriorated,




dismantle the vibrator-rapper rod assembly and inspect the




vibrator rod nipple for dust accumulation.  Packed dust in this




area will dampen the vibrations to the discharge wires and cause




excessive dust accumulation, close electrical clearances,  and




reduced precipitator performance.  Check the area where the




vibrator rapper rod passes through the packing ring retainer




plate for dust or for sign of inleakage of air and/or water.




This condition is indicative of a locse retainer plate providing




an inadequate seal between the packing and the vibrator-rapper




rod or of failure of the package rings.  A loose retainer  plate




should be tightened and in case of gas leakage,  the packing




should be replaced.




B.3.3  PLATE RAPPERS



     Check the rapper assemblies periodically for any possible




binding of the plunger or misalignment of assembly.  The maxim.um



amount of energy can be transmitted from ceil to plunger only




when the plunger is properly located with respect to the coil.




Any deviation will decrease the energy transmitted.  Adjusting




bolts allows changes of the distance between the lower casing and




the mounting and thereby allows variation of the plunger insertion




in the coil.
                               B-22

-------
     If the boot seal or  service sheet gasket has deteriorated,




dismantle the vibrator-rapper assembly and inspect the rapper rod



sleeve for dust accumulation.  Packed dust in this area will



dampen the shock wave to  the collecting plate and cause excessive



dust accumulation on the  plates  (wires).   [A boot seal is the



rubber seal that is stretch-fitted over the end of the rapper



rod.  On negative-pressure installations, the boot seal prevents



air and water from entering the precipitator chamber through the



rapper rod guide sleeve.  On positive-pressure installations, the



boot seal prevents precipitator gases from flowing up the rapper



and guide sleeve and entering the rapper coil tube.]



     Inspect striking end of plunger to ensure that the end has



not been flared or otherwise deformed due to excessive height in



its lift and/or misalignment.



     When reassembling the rapper assembly after maintenance has



been performed, make certain that the coil and coil cover are



plumb and level, and that the plunger is properly aligned in a



vertical plane on the rapper rod.



     The maintenance checks outlined above apply also to wire



rappers.



B.3.4  UPPER PRECIPITATOR



     Top Housing



     Inspect the fan to ensure that it is working and that the



filters are in good condition.



     Inspect vent elbows  for accumulation of foreign matter,




which would reduce or cut off the air flow.
                               B-23

-------
     Check access doors, inspecting the gaskets for signs of



deterioration and leaks.  Replace defective gaskets and lubricate



door lugs and hinges as required.




     Check that interlocks are clean, and lubricated with powder-



ed graphite.




     Inspect the upper rapper-rod vibrator on the high-tension



frame to ensure that it is centered in its guide nipple and that



no dust has packed between the nipple and the rapper-vibrator



rod.  If the rapper-vibrator rod needs to be centered in the



nipple, cover the insulator with an asbestos blanket, and with a



torch cut the nipple loose from the cold roof.   Reposition the



nipple, centering the rod, and reweld the nipple to the cold



roof.  Care must be taken that the new weld is  a complete seal;'



water and ambient air could flow through pinholes and contaminate




the insulators.



     Note:  Whenever, it is necessary to do any welding on the



high-tension wire supporting frame, the electrical bus connection



to the high-tension support b-shing shoul d be d i s connected..  A



heavy, temporary ground, sufficient to carry total welding cur-



rent, should be solidly connected to the high-tension frame.  The



disconnected bushing should be securely grounded at both ends,



i.e., in the rectifier ground switrh enclosure  and at the support




bushing end.



     Insulator Compartments



     Energize high-tension frame vibrators and  check for smooth



operation.  Check field wiring and vibrator control  cabinet if an






                              B-24

-------
inoperative vibrator is found.  Vibrator insulator nuts and all



pipe plugs should be secure.



     Check all nipples and seals.




     Inspect all dampers in the duct connections to the compart-



ments to ensure that they are in the open position.  Operate



pressurizing fan and check that air is flowing uniformly into



each insulator compartment.



     The vent elbow should be equipped with a pipe plug unless



the installation is operating under negative pressure.  If the



installation is under negative pressure, there should be no plug.



Inspect the elbow for dust and/or other foreign material.



     Inspect the pipe and guard through the inspection hatch to



ensure that the inside surface is free from dust accumulation



and/or rust and scale.   Remove all dust accumulations and/or rust



and scale buildups to prevent high-voltage arcing from the pipe



to the guard.   Inspect insulators to ensure that they are free



from cracks, chips, and dust accumulations.  Replace any cracked



or chipped insulators and clean dirty insulators with a nona-



brasive cleaner.



     Inspect the gasket on the inspection door for deterioration



and leaks; replace worn or leaky gaskets.  Make sure that all



bolts are in place and securely fastened.  Determine that inter-



lock is operable and well-lubricated with powdered graphite.



     Inspect upper vibrator-rapper rod - see Section 3.1.3.



     Inspect the vibrator-rapper rod insulator for dust accumu-



lation, chips, cracks,  and electrical tracking.  Electrical
                              B-25

-------
tracking that has not damaged the glazed surface of the insulator



and dust accumulations should be cleaned off with a nonabrasive



cleaner.  Replace cracked, chipped, or glaze-damaged insulators.



     Inspect the area between the vibrator-rapper rod and the



hanger pipe for packed dust accumulations.   Remove any accumula-



tion as it tends to dampen the vibration transmitted to the upper



high-tension frame.  Check to see that the vibrator-rapper rod is



centered in the support pipe.  If the support pipe is off center,



chances are that the weld between the lower vibratcr-rapper rod



and the upper high-tension frame has broken.  Recenter the rod



and reveId it to the high-tension frame.  As with the upper



vibrator-rapper rod, inspect the insulator clamp, ensuring that



all bolts are in place and tight.



     Check the high-tension frame support pipe.   Inspect the



round nut screwed onto the support pipe to prevent pipe r.cver.er.t.



     Remove the cover plates and inspect the inside and outside



surfaces of the support insulator for dust accumulations, elec-



trical tracking, cracks,  and chips.  Dust accumulations and



electrical tracking that  have not damaged the glazed surface of



the insulator should be cleaned with a nonabrasive cleaner.



     Plate Hanger Anvil Beam



     Inspect the anvil beam hanger rod clips to ensure that they



are straight.  Excessively heavy plate vibrating-rapping can in



time cause these clips to bend, causing the plate bank to shift



out of alignment.   This shift results in electrical clearances



out of tolerance and reduced precipitator performance.
                               B-26

-------
     Inspect the hanger rods to ensure that none are broken,




missing, or bent.  Broken, missing, or bent hanger rods usually



cause out-of-tolerance electrical clearance and reduced precipi-



tator performance.  Replace any defective hanger rods.



     Inspect the area behind the plate hanger anvil beam for



packed dust.  Remove dust, since it can force the beam out of



plumb.




     Inspect the weld between the vibrator-rapper rod and the



anvil beam.  If this weld is broken or cracked, it should be



replaced.



     Upper High-Tension Frame



     Check bolts and welds on the high-tension frame.



     Replace broken, bent, or missing support rods.



     Check wire support angles for broken welds where they



attach to the spacer beam.  Repair broken welds, making sure that



the wire support angles are parallel and on 9-inch centers (as-



suming 9 inch plate-to-plate spacing).



     Check to determine whether the high-tension frame is level



both perpendicular and parallel to the gas flow.  If the frame is



not level in the direction of gas flow, adjust at the appropriate



high-tension frame support rods.  If the frame is not level



perpendicular to the gas flow, adjust at the appropriate high-



tension frame hanger pipes.



     Check for excessive accumulation of dust on this frame.



Accumulations are excessive if they interfere with specified



clearances of 4-1/2 inches + 1/4 inch between the discharge wires
                               B-27

-------
and collecting plates or if they create a clearance of less than




4-1/2 inches between the high-tension frame and any other grounded




surface  (assuming 9 inch plate-to-plate spacing).




B.3.5  DISCHARGE WIRES




     Whenever possible, determine the condition of the discharge




wires with regard to dust buildup.   The amount of  buildup will




indicate whether the high-tension vibrators are operating at the




proper intensity.




     The discharge wires should be  kept as clean as is practical.




     Inadequate vibrating-rapping of the discharge wires can




result in heavy dust buildup,  with  localization of the corona




current and excessive sparking.




     A deposit on the discharge wires results from many things,




including poor gas distribution and characteristics of the dust.




Doughnut-shaped deposits often are  formed.  They are composed




generally of finer dust particles.   Deposits on the discharge




wires do net necessarily result in  poor performance, although



depending on resistivity, power supply ranee, and  uniformity of




the deposit, they can reduce efficiency.




     The discharge wires should be  perfectly centered between the




plates from top to bottom for  optimum precipitator operation.




Any broken discharge wires should be removed and if time permits,




replaced with new wires.  Since a cast iron weight is connected




to each wire at its lower end, a resistance will be felt when




pulling on the wire.  A wire that gives no resistance is broken.




     Broken wires can sometimes be  seen from catwalks located




between the collecting plate banks.  With a flashlight, look down



                               B-28

-------
each duct noting any bottle weight that is hanging on its bottle




guide and any wires that are out of alignment.



     The location of a broken wire that is removed but not



replaced should be recorded on a permanent log sheet.  This



recording will save time during future outages when time permits



the installation of a new wire.  A record of broken wire loca-



tions is also helpful in determining the cause of wire breakage,



i.e., if a number of wires break in the same area of the precipi-



tator, there are alignment problems.   If the wire breakage is



random, the breakage is probably caused by dust buildups on wires



or plates.



     The damaged wire may be cut away and the replacement wire



brought into the precipitator through the top upper high-tension



frame area, placed in the proper duct, lowered into place, and




attached.



B.3.6  COLLECTING PLATES



     Whenever the precipitator is out of service and internal



inspections are possible, the collecting plates should be checked



for proper alignment and spacing.  Check all hangers.  Make sure



that spacers at the bottom of the plates do not bind plates to



prevent proper rapping.  Check the lower portion of all plates



and the portion of plates adjacent to any door openings for signs



of corrosion.  If corrosion is present, it usually indicates air



inleakage through hoppers or around doors.



     Observe the dust deposits on the collecting plates before



starting any cleaning of the precipitator.  The normal thickness
                               B-29

-------
of collected dust is about 1/2 inch with occasional buildups of




1/4 inch.  If the buildup exceeds this amount, the intensity of




the plate vibratir.g-rapping should be increased.   If the col-




lection plates are almost metal clean, this may be an indication




cf high gas velocity, extremely coarse dust, too high a vibra-




tir.g-rapping intensity, or too low an operating voltage for good




precipitation.  This condition may be noted if a section has been




shorted out prior to the inspection.




     The plate may be in effect removed from service by removing




the discharge wires surrounding it.   When bellying or bowing of




tr.e plates is noted, the concave side of the plate may be heat-




treated with a torch, depending upon  the severity cf the de-




formity.




B.3.7  LOWER PRECIPITATOR STEADYING FRAME




     Inspect the steadying bars for cracked or broken welds where




they mount to the steadying bar support.  Perform any needed




repairs.



     .Make sure that the lower steadying frame is level both in




the direction of gas flow and perpendicular to gas flew.  If the




frare is net level, readjust the support wires, adjusting both




until the frame is level.  Place equal tension on each of the




support wires connected to adjusting  bolts, since slack wires




will cause excessive sparking.




     Inspect the steadying frame for downward bow in the stead-




ying bars (usually occurs after operating the precipitator  at




over-design temperatures).  Downward bows can usually be removed
                               B-30

-------
by cutting a wedge-shape slot in the vertical member of the



steadying bar angle, pushing with jacks or pulling with a block



and tackle until the frame is straight, then welding an addi-



tional piece of angle iron inside the steadying bar angle and



across the wedge slot.




     Inspect the steadying frame for twisting.  A twisted frame



causes excessive weight on some wires and slackness in others.



To straighten a twisted frame, grasp one end of the frame and



twist the frame until that end is straight and level.  While



holding the frame in this position, weld the frame to the hopper



walls.  Repeat for the other end of the frame.  Once the frame



has been welded to the hopper walls and is straight and level,



using a torch, stress-relieve the frame by heating each con-



nection between the steadying bar supports and the steadying bars



until it glows to a cherry red.  After all joints have been



relieved, allow the frame to cool, then cut it free of the hopper



walls.  If the frame is still twisted, repeat the procedure.  If



after the second heating the frame is still twisted, a new frame



will have to be installed.



     When checking the lower steadying frame anti-sway insula-



tors, check the surface for dust accumulation, glaze damage



caused by electrical tracking, cracks, and chips.  Insulators



with dust accumulation and/or electrical tracking that has not



damaged the glazed surfaces may be cleaned with a nonabrasive



cleaner.  Cracked, chipped, broken, or glaze-damaged insulators




may be replaced.
                               B-31

-------
B.3.8  DUST COLLECTION POINT




     In electrostatic precipitators servicing recovery furnaces,




the precipitator bottom can be one of two designs -- dry and wet.




The dry drag bottom can be constructed as a flat bottom col-




lecting chamber underneath the precipitator plates.   From there




the collected material is removed by means of drag scraper and




screw conveyor and finally discharged into a rotary  valve.  The




use of trough hoppers with screw conveyors and rotary discharge




valves is another method of collecting dust from dry bottom




electrostatic precipitatcrs.   The wet bottom construction is




associated with the conventional recovery process.




     Try 2ra_g Bottoms




     It is extremely important that all bearings be  lube-purged




after every precipitator washdown.  In the worm gear speed re-




ducer, the oil case should be thoroughly flushed with a light




flushing oil before refilling.  An oil change every  two to three




months is recommended thereafter.  Check the oil level in both



the high speed and low speed  chambers before operating.  Check




periodically, with redjcer at rest, to deter~ir.e whether the oil




is at the proper level.  The  slow speed shaft bearings should be




lubricated with a lithium, based grease.  The motor bearings are




prelubed prior to shipment.  However, where the motor is used




constantly in a dirty or wet  environment, it is advisable to add




one quarter ounce of lithium  based bearing grease per bearing




every three months.  Where it is necessary to add grease, stop




the motor.  The Rex bearings  should be examined and  relubricated
                              B-32

-------
at least every six months.  The Roller chain should be lubricated



manually with a brush or spout type oil can maintaining a clean



oil film at all load carrying points where relative motion occurs



to assure maximum operating efficiency.  These points are between



the pin and bushing, bushing and roller, and the roller and the



sprocket teeth.  Oil should be directed to the inside of the



lower span of chain in the spaces between the side bars.  The



motor coupling is prelubed, but periodic inspections should be



made to assure that the coupling contains lubrication.



     Wet Bottom



     During periodic precipitator shutdowns, all of the liquor



should be drained into the wet bottom pan.  In this way all



accumulations of saltcake present on the floor of the wet bottom



can be removed.  Periodic check should be made of the structural



soundness and tightness of the acid proof lining on the vertical



sides of the pan.  Check the oil level in the gear reducer of the



agitator drive.  The bearings should be greased and checked.  The



wet bottom liquor level control consists of an external float



chamber with a float actuated level controller.  Occasionally,



soap will accumulate in the float chamber which should be cleaned



out at frequent intervals.  To prevent the black liquor from



congealing in the float chamber, it is important that a small



supply of hot liquor be continually fed to the float tank.



     Hoppers



     The dust collecting system in bark and combination bark/



fossil fuel fired boilers consists of pyramidal and trough hop-

-------
pers.  It is extremely important to establish a regular schedule



of hopper emptying at the start of operation and adhere to it as



closely as possible, preferably once a shift.  If the hoppers are



allowed to fill over a 24-hour period or longer, the electrical



components may short out and precipitation will cease.   Also, if



a fly ash hopper is allowed to stand for more than 24 hours, the



dust tends to pack, cool off, and absorb some moisture  from the



cases.  The principal problems with hoppers are 1)  corrosion and



2) difficulty with free-flowing of the dust from the hcppers.



Both problems may be partially overcome by proper steam tracing



and heat insulation of the hopper exterior, subsequent  care that



a constant steam supply to the hopper coils is being maintained,



and that damaged heat insulation is properly repaired.   Any



abnormal buildups should be removed.  If this condition becomes



chronic, it is an indication of low operating temperatures,



insufficient heat insulation, or inadequate hopper emptying.



Also it should be noted that because of the carbonaceous nature



cf tr.is dust, excessive accumulation in pyramidal hoppers can



become a fire hazard.



     Screw Ccnveypr System



     In recovery furnace applications saltcake is normally



removed by means of screw conveyors.  In the bark and combination



bark fossil fuel-fired boilers, dust is removed by a vacuum,



conveying system.  The dust is aspirated out, mixed with water  to



form a slurry, and then transported away.  In the screw conveyor



system it is important to establish routine periodic inspections
                              B-34

-------
of the entire conveyor to insure continuous maximum operating



performance.  Important items to check are intake and discharge



points, flight thickness at the outer edge, and condition of



bearings.



B.3.9  PRECIPITATOR SHELL



     The flue gases, emanating from the kraft pulp mill process,



contain certain acidic constituents which are extremely corrosive



to steel.  Temperature control is of prime importance in keeping



corrosion at a minimum.  Corrosion can become quite extensive if



interior surfaces become cool for any reason.  It is therefore



recommended that thorough internal inspections be made during the



first year of operation.  If interior corrosion is noted, some



means of correction should be applied as soon as possible.  Heat



insulation applied to exteriors of the corroded components will



normally correct this condition.



     In kraft pulp mills, process operations can fluctuate



widely.  Covering the interior surfaces of side frames, end



frames, and roof with gunite will prevent damage to the steel.



The corrosive effects can be minimized by installing heat jackets



which can be heated by dry air or electric heat.



B.3.10  MAINTENANCE SCHEDULE AND TROUBLESHOOTING



     Annual Inspection/Maintenance



     Prior to any inspection, it is of utmost importance that the



precipitator is de-energized and grounded and the necessary



precautions are taken to ensure that the equipment control be



energized during the internal inspection.





                              B-35

-------
     Dust Accumulations




     Observe the dust accumulations on both plates and wires.




The discharge wires should have only a slight coating of dust




with no corona tufts  (doughnut-shaped dust accumulations).




Thickness of dust buildup on plates is normally between 1/8 and




1/4 inch.  If the plates have r.ore than 1/4 inch of dust, the




vibrator-rappers are not cleaning properly.




     Pi scharge Wires_




     Replace any broken discharge wires, necked-down wires, or




fatigued wires to avoid the possibility cf breaking during opera-




tion.  Breakage cf ;ust one wire may render an entire precipita-




tcr section inoperative.  Record the exact location of all wire




failures as well as the location of breakage on the wire.




     AjLigj"..~er.t cf_ Plates and__WjLr_e_s




     The plate-to-wire clearance at both top and bottom of




plates should not be less than 4-1/2 inches, while the rir.imum




acceptable plate-to-wire clearance at the vertical midpoint cf




the plates is 4 inches  (assuring 9-inch duct spacing).  Close




electrical clearances create excessive sparking and prevent




cptiru.T. operation.



     High-Ten_s icn and Plate_ _V_i_b_ra_tor_s-Rappers




     Check all high-tension and plate vibrators-rappers  for




misalignment and/or binding of the vibrator-rapper rods  through




the roof sleeves.  Binding in this area prevents transmission  of




rapper energy to the collecting plates and high-tension  discharge




wires and results in excessive dust accumulations.
                               B-36

-------
     High-Tension Frame Support Bushing



     The internal and external surfaces of the high-tension frame



support bushing must be maintained free of dust to guard against



high-voltage electrode tracking across insulator surfaces.   This



condition will lead to thermal fracturing of the bushings through



heat concentration.  Clean all high-voltage insulators and check



thoroughly for sign of cracks; replace where necessary.   All



electrical connections should be secure.



     High-Voltage Electrical Control Cabinet



     Clean all components of dust accumulation and lubricate



where necessary.   Replace the ventilating fan filter.



     Transformer-Rectifier Sets



     Check the oil level in the high-voltage transformer and add



the proper oil if necessary.  Check all bushings, terminals, and



insulators for dust buildup and evidence of electrical tracking.



Check the surge arrester gap setting on the high-voltage trans-



former and readjust if necessary.  Interlocks must also be




checked.



     Dry Drag Bottom



     The pillow block shaft bearing is a double row roller



bearing pre-lubed with sufficient lubrication for approximately




one year of normal service.



     Hoppers



     Hoppers are present on electrostatic precipitators servicing



bark and combination bark fossil fuel fired boilers.  Items to



check are dust buildup in the upper corners of hoppers and debris






                              B-37

-------
such as fallen wires and weights in the hopper bottom and valves.




Inspect anti-sway insulators to see that they are clean and not




cracked.  If a discharge electrode weight has dropped 3 inches,




it indicates a broken wire.




     Screw Conveyor




     Since the highest torque is transmitted at the drive shaft




and conveyer connection, it is recommended that coupling bolts be




removed periodically to inspect for widening of bolt holes and




ber.t cr worn belts.




     2ai ly_ !_.-: spect i_on_ ajnd_ Hea_dings




     Record all control set electrical readings once per shift.




Any abnormalities in shift-to-shift readings may well be the




first clue of a malfunction within the precipitator.   In addi-




tion, the daily log should include process operating data, flue




gas analysis, verification of transmissometer calibration, and a




record of all transm.issoneter readings.




     Vibrat_cr s 'Rappers




     Ensure that all collecting plate and discharge wire  (high-




tension )  vibrators-rappers are functioning properly and operating




at the proper intensity level.  Lack of vibrating/rapping will




result in dust buildup on both the plates and wires, which re-




duces electrical clearances and necessitates operation of the




equipment at reduced power levels.  Over vibrating,'ever rapping




of the internals leads to reentrainnent of collected dust; there-




fore, it is important that proper intensity values be used for




optimum precipitatcr performance.
                              B-38

-------
     Wet Bottom  (Conventional)




     Check the temperature of the piping between the wet bottom



and the float chamber to detect liquor congealment in the piping.



     Hoppers




     Thoroughly check all hoppers, particularly the unloading



mechanism for proper operation.  Overfilling of hoppers can lead



to very serious damage of internal components.  Check thoroughly



for air inleakage at the hoppers.   The siphoning of cold ambient



air into the hoppers usually results in formation of condensation



and agglomeration of dust, resulting in plugging of the hopper.



     A troubleshooting chart for an electrostatic precipitator is



presented in Table B.3-1.



     Frequency of failure of various precipitator components and



repair times for a typical industrial precipitator are presented



in Table B.3-2.
                              B-39

-------
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                            REFERENCES
1.   Henderson,  J.S.,  "Frecipitator Survey on Non-Contact Recovery
     Boilers, TAPPI Vol.  58 No.  5,  May 1975.

2.   Industrial  Air Pollution Control, Chapter 7,  FEDCo Environ-
     rer.tal, Inc., prepared for  U.S.  Environmental Research In-
     fcrration Center,  EPA 625/6-7S-004,  June 1978.
                               B-44

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                                 TECHNICAL REPORT DATA
                          (Please read Inuruciions on the rcvirsc bcjore completing)
1. REPORT NO.
 EPA-600/2-78-210
                            2.
                                                        3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
 Operation and Maintenance of Particulate Control
  Devices in Kraft Pulp Mill and Crushed Stone
  Industries	
                                                        5 REPORT DATE
                                                        October 1978
                                 6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
                                                        8. PERFORMING ORGANIZATION RLPORT NO.
 M. F. SzaboandR.W. Gerstle
9. PERFORMING ORGANIZATION NAME AND ADDRESS
 PEDCo.  Environmental Specialists,  Inc.
 11499 Chester Road
 Cincinnati, Ohio 45246
                                 10. PROGRAM ELEMENT NO.
                                  1AB012; ROAP 21ADL-037
                                 11. CONTRACT/GRANT NO.
                                  68-02-2105
12 SPONSORING AGENCY NAME AND ADDRESS
 EPA, Office of Research and Development
 Industrial Environmental Research Laboratory
 Research Triangle Park, NC  27711
                                 13. TYPE OF REPORT AND PERIOD COVERED
                                  Final; 6/77 - 7/78	
                                 14. SPONSORING AGENCY CODE
                                   EPA/600/13
15. SUPPLEMENTARY NOTES ffiRL-RTP project officer is Dennis C. Drehmel, Mail Drop 61,
 919/541-2925.
i6. ABSTRACT The repor(. addresses the control of fine particulate emissions from selec-
 ted kraft pulp mill and stone crushing facilities.  The principal devices considered
 are electrostatic precipitators, wet scrubbers, and fabric filters.  Guidelines are
 provided for industrial personnel responsible for selecting an appropriate control
 device.  Information on the operation and expected performance of conventional air
 pollution control devices Is based on current design practice, theoretical design
 models, reported performance,  cost predictions, and published information.
17.
                              KEY WORDS AND DOCUMENT ANALYSIS
                 DESCRIPTORS
                                           b.IDENTIFIERS/OPEN ENDED TERMS
                                              c. COSATI field/Group
 Air Pollution
 Dust
 Sulfate Pulping
 Crushed Stone
 Electrostatic Precip-
  itators
Scrubbers
Filtration
Fabrics
Air Pollution Control
Stationary Sources
Particulate
Kraft Pulp Mills
Wet Scrubbers       '
Fabric Filters
13B
11G       07 D
13H,07A  11E
13C

131
18. DISTRIBUTION STATEMENT

 Unlimited
                     19. SECURITY CLASS (This Report)
                     Unclassified
                                                                     21. NO. OF PAGES
                     20. SECURITY CLASS (Thispage)
                     Unclassified
                                              22. PRICE
EPA Form 2220-1 (9-73)

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